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Full text of "The history of creation, or, The development of the earth and its inhabitants by the action of natural causes : doctrine of evolution in general, and of that of Darwin, Goethe, and Lamarck in particular / from the German of Ernst Haeckel ; the translation revised by E. Ray Lankester"

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WisroRY of Creation 








+■ a 

By the same Author. 

By Professor E. Haeckel. Translated by E. A. 
J. Van Bhtn and L. Elsbekg, M.D. 

Now Beady. 
By Professor Oscar Schmidt (Strasburg Uni- 
versity). Illustrated. Price 5s. 

Being Vol. XII. of the International Scientific Series. 


Development of a Calcareous Sponge ( Olvnthus ") 


\ 6 1 






1 6 FEB 1998 













VOL. I. 

Henry S. King & Co., London. 


A sense sublime 
Of something far more deeply interfused, 
Whose dwelling is the light of setting suns, 
And the round ocean, and the living air, 
And the blue sky, and in the mind of man ; 
A motion and a spirit that impels 
All thinking things, all objects of all thought, 
And rolls through all things. 

In all things, in all natures, in the stars 
Of azure heaven, the unenduring clouds, 
In flower and tree, in every pebbly stone 
That paves the brooks, the stationary rocks, 
The moving waters and the invisible air. 


{All rights reserved.") 





General Importance and Essential Nature of the Theory of Descent as 
reformed by Darwin. — Its Special Importance to Biology (Zoology 
and Botany). — Its Special Importance to the History of the Natural 
Development of the Human Race. — The Theory of Descent as the 
Non-Miraculous History of Creation. — Idea of Creation. — Know- 
ledge and Belief . — History of Creation and History of Development. 
— The Connection between the History of Individual and Palseonto- 
logical Development. — The Theory of Purposelessness, or the 
Science of Rudimentary Organs. — Useless and Superfluous Ar- 
rangements in Organisms. — Contrast between the two entirely 
Opposed Views of Nature : the Monistic (mechanical, causal) and 
the Dualistic (teleological, vital). — Proof of the former by the 
Theory of Descent. — Unity of Organic and Inorganic Nature, and 
the Identity of the Active Causes in both. — The Importance of 
the Theory of Descent to the Monistic Conception of all Nature ... 1 



The Theory of Descent, or Doctrine of Filiation, as the Monistic Ex- 
planation of Organic Natural Phenomena. — Its Comparison with 
Newton's Theory of Gravitation. — Limits of Scientific Explanation 
and of Human Knowledge in general. — All Knowledge founded 
originally on Sensuous Experience, d posteriori. — Transition of a 
posteriori knowledge, by inheritance, into d priori knowledge. — 
Contrast between the Supernatural Hypotheses of the Creation ac- 

VOL. I. b 



cording to Linnaeus, Cuvier, Agassiz, and the Natural Theories of 
Development according to Lamarck, Goethe, and Darwin. — Con- 
nection of the former with the Monistic (mechanical), of the latter 
with the Dualistic Conception of the Universe. — Monism and 
Materialism. — Scientific and Moral Materialism. — The History of 
Creation according to Moses. — Linnaeus as the Founder of the Sys- 
tematic Description of Nature and Distinction of Species. — Linnaeus' 
Classification and Binary Nomenclature. — Meaning of Linnaeus' Idea 
of Species. — His History of Creation. — Linnaeus' view of the Origin 
of Species ... ... ... ... ... ... ... ... 24 



General Theoretical Meaning of the Idea of Species. — Distinction be- 
tween the Theoretical and Practical Definition of the Idea of Species. 
— Cuvier's Definition of Species. — Merits of Cuvier as the Founder 
of Comparative Anatomy. — Distinction of the Four Principal Forms 
(types or branches) of the Animal Kingdom, by Cuvier and Bar. — 
Cuvier's Services to Palaeontology. — His Hypothesis of the Revo- 
lutions of our Globe, and the Epochs of Creation separated by them. 
— Unknown Supernatural Causes of the Revolutions, and the sub- 
sequent New Creations. — Agassiz's Teleological System of Nature. 
— His Conception of the Plan of Creation, and its six Categories 
(groups in classification). — -Agassiz's Views of the Creation of 
Species. — Rude Conception of the Creator as a man-like being 
in Agassiz's Hypothesis of Creation. — Its internal Inconsistency 
and Contradictions with the important Palaeontological Laws dis- 
covered by Agassiz ... ... ... ... ... ... ... 47 



Scientific Insufficiency of all Conceptions of a Creation of Individual 
Species — Necessity of the Counter Theories of Development. — 
Historical Survey of the most Important Theories of Development. 
— Aristotle. — His Doctrine of Spontaneous Generation. — The 
Meaning of Nature-philosophy. — Goethe. — His Merits as a 
Naturalist. — His Metamorphosis of Plants. — His Vertebral Theory 
of the Skull. — His Discovery of the Mid Jawbone in Man. — 
Goethe's Interest in the Dispute between Cuvier and Geofiroy 



St. Hilaire. — Goethe's Discovery of the two Organic Formative 
Principles, of the Conservative Principle of Specification (by In- 
heritance), and of the Progressive Principle of Transformation (by 
Adaptation). — Goethe's Views of the Common Descent of all Ver- 
tebrate Animals, including Man. — Theory of Development according 
to Gottfried Eeinhold Treviranus. — His Monistic Conception of 
Nature. — Oken. — His Nature-philosophy. — Oken's Theory of 
Protoplasm. — Oken's Theory of Infusoria (Cell Theory). — Oken's 
Theory of Development ... ... ... ... ... ... 72 




Kant's Dualistic Biology. — His Conception of the Origin of Inorganic 
Nature by Mechanical Causes, of Organic Nature by Causes acting 
for a Definite Purpose. — Contradiction of this Conception with his 
leaning towards the Theory of Descent. — Kant's Genealogical 
Theory of Development. — Its Limitation by his Teleology. — Com- 
parison of Genealogical Biology with Comparative Philology. — 
Views in favour of the Theory of Descent entertained by Leopold 
Buch, Bar, Schleiden, Unger, Schaafhausen, Victor Cams, Buchner. 
— French Nature-philosophy. — Lamarck's Philosophie Zoologique. — 
Lamarck's Monistic (mechanical) System of Nature. — His Views 
of the Inter-action of the two Organic Formative Tendencies of 
Inheritance and Adaptation. — Lamarck's Conception of Man's 
Development from Ape-like Mammals. — Geoffroy St. Hilaire's, 
Naudin's, and Lecoq's Defence of the Theory of Descent. — English 
Nature-philosophy. — Views in favour of the Theory of Descent 
entertained by Erasmus Darwin, W. Herbert, Grant, Freke, Herbert 
Spencer, Hooker, Huxley. — The Double Merit of Charles Darwin . . . 100 



Charles Lyell's Principles of Geology. — His Natural History of the 
Earth's Development. — Origin of the Greatest Effects through the 
Multiplication of the Smallest Causes. — Unlimited Extent of Geo- 
logical Periods. — Lyell's Refutation of Cuvier's History of Creation. 
— The Establishment of the Uninterrupted Connection of Historical 
Development by Lyell and Darwin. — Biographical Notice of Charles 
Darwin. — His Scientific Works. — His Theory of Coral Reefs. — De- 



velopment of the Theory of Selection. — A Letter of Darwin's. — 
The Contemporaneous Appearance of Darwin's and Alfred Wallace's 
Theory of Selection. — Darwin's Study of Domestic Animals and 
Cultivated Plants. — Andreas Wagner's Notions as to the Special 
Creation of Cultivated Organisms for the good of Man. — The Tree 
of Knowledge in Paradise. — Comparison between Wild and Culti- 
vated Organisms. — Darwin's Study of Domestic Pigeons. — Import- 
ance of Pigeon Breeding. — Common Descent of all Eaces of 
Pigeons ... ... ... ... ... ... ... ... ... 125 



Darwinism (Theory of Selection) and Lamarckism (Theoiy of Descent) . 
— The Process of Artificial Breeding. — Selection of the Different 
Individuals for After-breeding. — The Active Causes of Transmuta- 
tion. — Change connected with Food and Transmission by Inheritance 
connected with Propagation. — Mechanical Nature of these Two 
Physiological Functions. — The Process of Natural Breeding : 
Selection in the Struggle for Existence. — Malthus' Theory of 
Population. — The Proportion between the Numbers of Potential 
and Actual Individuals of every Species of Organisms. — General 
Struggle for Existence, or Competition to attain the Necessaries of 
Life. — Transforming Force of the Struggle for Existence. — Com- 
parison of Natural and Artificial Breeding — Selection in the Life of 
Man. — Military and Medical Selection ... ... ... ... 149 


Universality of Inheritance and Transmission by Inheritance. — Special 
Evidences of the same. — Human Beings with four, six, or seven 
Fingers and Toes. — Porcupine Men. — Transmission of Diseases, 
especially Diseases of the Mind. — Original Sin. — Hereditary 
Monarchies. — Hereditary Aristocracy. — Hereditary Talents and 
Mental Qualities. — Material Causes of Transmission by Inheritance. 
— Connection between Transmission by Inheritance and Propaga- 
tion. — Spontaneous Generation and Propagation. — Nonsexual or 
Monogonous Propagation. — Propagation by Self -Division. — Monera 
and Amoeba. — Propagation by the formation of Buds, by the for- 
mation of Germ-Buds, by the formation of Germ-Cells. — Sexual or 
Amphigonous Propagation. — Formation of Hermaphrodites. — Dis- 
tinction of Sexes, or Gonochorism. — Virginal Breeding, or Parthe- 



nogenesis. — Material Transmission of Peculiarities of both Parents 
to the Child by Sexual Propagation. — Difference between Trans- 
mission by Inheritance in Sexual and in Asexual Propagation . . . 175 



Distinction between Conservative and Progressive Transmission by In- 
heritance. — Laws of Conservative Transmission : Transmission of 
Inherited Characters. — Uninterrupted or Continuous Transmission. 
— Interrupted or Latent Transmission. — Alternation of Generations. 
■ — Eelapse. — Degeneracy. — Sexual Transmission. — Secondary 
Sexual Characters. — Mixed or A mphigonous Transmission. — 
Hybrids. — Abridged or Simplified Transmission. — Laws of Pro- 
gressive Inheritance : Transmission of Acquired Characters. — 
Adapted or Acquired Transmission. — Fixed or Established Trans- 
mission. — Homochronous Transmission (Identity in Epoch). — 
Homotopic Transmission (Identity in Part) . — Adaptation and 
Mutability. — Connection between Adaptation and Nutrition. — Dis- 
tinction between Indirect and Direct Adaptation ... . . , ... 203 



Laws of Indirect or Potential Adaptation. — Individual Adaptation. — 
Monstrous or Sudden Adaptation. — Sexual Adaptation. — Laws of 
Direct or Actual Adaptation. — Universal Adaptation. — Cumulative 
Adaptation. — Cumulative Influence of External Conditions of Ex- 
istence and Cumulative Counter-Influence of the Organism. — Free 
Will.: — Use and Non-use of Organs. — Practice and Habit. — Cor- 
relative Adaptation. — Correlation of Development. — Correlation of 
Organs. — Explanation of Indirect or Potential Adaptation by the 
Correlation of the Sexual Organs and of the other parts of the 
Body. — Divergent Adaptation. — Unlimited or Infinite Adaptation... 227 



Interaction of the two Organic Formative Causes, Inheritance and 
Adaptation. — Natural and Artificial Selection. — Struggle for Ex- 
istence, or Competition for the Necessaries of Life. — Disproportion 



between the Number of Possible or Potential, and the Number of 
Eeal or Actual Individuals. — Complicated Correlations of all Neigh- 
bouring Organisms. — Mode of Action in Natural Selection. — Homo- 
chromic Selection as the Cause of Sympathetic Colourings. — 
Sexual Selection as the Cause of the Secondary Sexual Characters. 
— Law of Separation or Division of Labour (Polymorphism, Differ- 
entiation, Divergence of Characters) . — Transition of Varieties into 
Species. — Idea of Species. — Hybridism. — Law of Progress or Per- 
fecting (Progressus, Teleosis) ... ... ... ... ... ... 252 



Laws of the Development of Mankind : Differentiation and Perfecting. 
— Mechanical Cause of these two Fundamental Laws. — Progress 
without Differentiation, and Differentiation without Progress. — 
Origin of Rudimentary Organs by Non-use and Discontinuance of 
Habit. — Ontogenesis, or Individual Development of Organisms. — 
Its General Importance. — Ontogeny, or the Individual History of 
Development of Vertebrate Animals, including Man. — The Fructi- 
fication of the Egg. — Formation of the Three Germ Layers. — 
History of the Development of the Central Nervous System, of the 
Extremities, of the Branchial Arches, and of the Tail of Vertebrate 
Animals. — Causal Connection and Parallelism of Ontogenesis and 
Phylogenesis, that is, of the Development of Individuals and Tribes. 
— Causal Connection of the Parallelism of Phylogenesis and of 
Systematic Development. — Parallelism of the three Organic Series 
of Development ... ... ... ... ... ... ... ... 280 



History of the Development of the Earth. — Kant's Theory of the De- 
velopment of the Universe, or the Cosmological Gas Theory. — 
Development of Suns, Planets, and Moons. — First Origin of Water. 
— Comparison of Organisms and Anorgana. — Organic and Inorganic 
Substances. — Degrees of Density, or Conditions of Aggregation. — 
Albuminous Combinations of Carbon. — Organic and Inorganic 
Forms. — Crystals and Formless Organisms without Organs. — 



Stereometrical Fundamental Forms of Crystals and of Organisms. — 
Organic and Inorganic Forces. — Vital Force. — Growth and Adapta- 
tion in Crystals and in Organisms. — Formative Tendencies of 
Crystals. — Unity of Organic and Inorganic Nature. — Spontaneous 
Generation, or Archigony. — Autogony and Plasmogony. — Origin of 
Monera by Spontaneous Generation. — Origin of Cells from Monera. 
— The Cell Theory. — The Plastid Theory. — Plastids, or Structural- 
Units. — Cytods and Cells. — Four Different Kinds of Plastids ... 316 



Chorological Facts and Causes. — Origin of most Species in one Single 
Locality. — "Centres of Creation." — Distribution by Migration. — 
Active and Passive Migrations of Animals and Plants. — Means of 
Transport. — Transport of Germs by Water and by Wind. — Con- 
tinual Change of the Area of Distribution by Elevations and 
Depressions of the Ground.— Chorological Importance of Geological 
Processes. — Influence of the Change of Climate. — Ice or Glacial 
Period. — Its Importance to Chorology. — Importance of Migrations 
for the Origin of New Species. — Isolation of Colonists. — Wagner's 
Law of Migration. — Connection between the Theory of Migration 
and the Theory of Selection. — Agreement of its Results with the 
Theory of Descent ,,, ... ... ... 350 




Development of a Calcareous Sponge (Olynthus) Frontispiece 

I.— Life History of a Simplest Organism To face page 184 

II., III. — Germs or Embryos of Four Vertebrates ... „ 306 


1. — Propagation of Moneron 

2. — Propagation of Amoeba ... 

3. — Egg of Mammal 

4. — First Development of Mammal's Egg 
5. — The Hnman Egg Enlarged 
6. — Development of Mammal's Egg 
7. — Embryo of a Mammal or Bird ... 

••■ ••« •■• • 

. 186 

... ... •.. • 

. 188 

••• ••• ••• • 

. 189 

... ••« • 

. 190 

... •<• ••• • 

.. 297 

... ••> ... • 

. 299 

. C04 


I AM desirous of prefacing the English edition of the 
" History of Creation " with a few remarks which may serve 
to explain the origin and object of this book. In the year 
1866 I published, under the title " Generelle Morphologic," 
a somewhat comprehensive work, which constituted the first 
attempt to apply the general doctrine of development to the 
whole range of organic morphology (Anatomy and Biogenesis), 
and thus to make use of the vast march onwards which the 
genius of Charles Darwin has effected in all biological 
science by his reform of the Descent Theory and its esta- 
blishment through the doctrine of selection. At the same 
time, in the " Generelle Morphologie," the first attempt was 
made to introduce the Descent Theory into the systematic 
classification of animals and plants, and to found a " natural 
system " on the basis of genealogy ; that is, to construct 
hypothetical pedigrees for the various species of organisms. 

The " Generelle Morphologie " found but few readers, for 
which the voluminous and unpopular style of treatment, and 
its too extensive Greek terminology, may be chiefly to blame. 
But a proportionately large measure of approval has met 


the " Naturliche Schopfungsgeschichte " in Germany. This 
book took its origin in the shorthand notes of a course of 
lectures which treated, before a mixed audience and in 
a popular form, the most important topics discussed in the 
"Generelle Morphologic" The notes were subsequently 
revised, and received considerable additions. The book 
appeared first in 1868, its fourth edition in 1873, and has 
been translated into several languages. I hope that it may 
also find sympathy in the fatherland of Darwin, the more so 
since it contains special morphological evidence in favour of 
many of the important doctrines with which this greatest 
naturalist of our century has enriched science. Proud as 
England may be to be called the fatherland of Newton, who, 
with his law of gravitation, brought inorganic nature under 
the dominion of natural laws of cause and effect, yet may 
she with even greater pride reckon Charles Darwin among 
her sons — he who solved the yet L harder problem of bring- 
ing the complicated phenomena of organic nature under the 
sway of the same natural laws. 

The reproach which is now offcenest made against the 
Descent Theory is that it is not securely founded, not suffi- 
ciently proven. Not only its distinct opponents maintain that 
there is a want of satisfactory proofs, but even faint-hearted 
and wavering adherents declare that Darwin's hypothesis is 
still wanting fundamental proof. Neither the former nor the 
latter estimate rightly the immeasurable weight which the 
great series of phenomena of comparative anatomy and onto- 
geny, palseontology and taxonomy, chorology and cecology, 
cast into the scale in favour of the doctrine of filiation. 
Darwin's Theory of Selection, which completely explains the 
origin of species through the combined action of Inheritance 


and Adaptation in the struggle for existence, also appears to 
these persons not sufficient. They demand, over and above, 
that the descent of species from common ancestral forms 
shall be proved in a particular case ; that, in contradistinc- 
tion to the synthetic proofs adduced for the Descent Theory, 
the analytic proof of the genealogical continuity of the 
several species shall be brought forward. 

This " analytical solution of the problem of the origin of 
species " I have myself endeavoured to afford in my recently 
published " Monograph of the Calcareous Sponges." For five 
consecutive years I have investigated this small but highly 
instructive group of animals in all its forms in the most 
careful manner, and I venture to maintain that the mono- 
graph, which is the result of those studies, is the most 
complete and accurate morphological analysis of an entire 
organic group which has up to this time been made. 
Provided with the whole of the material for study as yet 
brought together, and assisted by numerous contributions 
from all parts of the world, I was able to work over the 
whole group of organic forms known as the Calcareous 
Sponges in that greatest possible degree of fulness which 
appeared indispensable for the proof of the common origin 
of its species. This particular animal group is especially 
fitted for the analytical solution of the species problem, 
because it presents exceedingly simple conditions of organ- 
ization, because in it the morphological conditions possess a 
greatly superior, and the physiological conditions an inferior, 
import, and because all species of Calcispongise are remark- 
able for the fluidity and plasticity of their form. With a 
view to these facts, I made two journeys to the sea-coast 
(1869 to Norway, 1871 to Dalmatia), in order to study as 


large a number of individuals as possible in their natural 
circumstances, and to collect specimens for comparison. Of 
many species, I compared several hundred individuals in the 
most careful way. I examined with the microscope and 
measured in the most accurate manner the details of form of 
all the species. As the final result of these exhaustive 
and almost endless examinations and measurements it 
appeared that "good species," in the ordinary dogmatic 
sense of the systematists, have no existence at all among 
the Calcareous Sponges ; that the most different forms are 
connected one with another by rmmberless gradational 
transition forms ; and that all the different species of Calca- 
reous Sponges are derived from a single exceedingly simple 
ancestral form, the Olynthus. A drawing of the Olynthus 
and its earliest stages of development (observe especially the 
highly important Gastrula) is given in the frontispiece of 
the present edition. Illustrations of the various structural 
details which establish the derivation of all Calcareous 
Sponges from the Olynthus, are given in the atlas of 
sixty plates which accompanies my monograph of the 
group. In the gastrula, moreover, is now also found the 
common ancestral form from which all the tribes of animals 
(the lowest group, that of the protozoa, alone being excepted) 
can without difficulty be derived. It is one of the most 
ancient and important ancestors of the human race ! 

If we take for the limitation of genus and species an average 
standard, derived from the actual practice of systematists, and 
apply this to the whole of the Calcareous Sponges at present 
known, we can distinguish about twenty-one genera, with one 
hundred and eleven species (as I have done in the second 
volume of the Monograph). I have, however, shown that we 


may draw up, in addition to this, another systematic arrange- 
ment (more nearly agreeing with the arrangement of the Calci- 
spongiee hitherto in vogue) which gives thirty-nine genera 
and two hundred and eighty-nine species. A systematist 
who gives a more limited extension to the " ideal species " 
might arrange the same series of forms in forty -three genera 
and three hundred and eighty-one species, or even in one 
hundred and thirteen genera and five hundred and ninety 
species ; another systematist, on the other hand, who takes a 
wider limit for the abstract *-' species," would use in arrang- 
ing the same series of forms only three genera, with twenty- 
one species, or might even satisfy himself with one genus 
and seven species. The delimitation of species and genera 
appears to be so arbitrary a matter, on account of endless 
varieties and transitional forms in this group, that their 
number is entirely left to the subjective taste of the indi- 
vidual systematist. In truth, from the point of view of the 
theory of descent, it appears altogether an unimportant ques- 
tion as to whether we give a wider or a narrower signifi- 
cation to allied groups of forms — whether we choose, that is 
to say, to call them genera or species, varieties or sub-species. 
The main fact remains undeniable, viz., the common origin 
of all the species from one ancestral form. The many- 
shaped Calcareous Sponges furnish, in the very remarkable 
conditions of their varieties of aggregation (metrocormy), a 
body of evidence in favour of this view which could hardly 
be more convincing. Not unfrequently the case occurs of 
several different forms growing out from a single " stock " 
or " cormus " — forms which until now have been regarded 
by systematists, not only as belonging to different species, 
but even to different genera. Fig. 10 in the frontispiece 


represents such a composite stock. This solid and tangible 
piece of evidence in favour of the common descent of 
different species ought, one would think, to satisfy the most 
determined sceptic ! 

In point of fact, I have a right to expect of my opponents 
that they shall carefully consider the " exact empirical proof" 
here brought forward for them, as they have so eagerly 
demanded. The opponents of the doctrine of filiation, who 
have too little power of weighing evidence, or possess too 
little knowledge to appreciate the overpowering weight of 
proof afforded by the synthetical argument (comparative 
anatomy, ontogeny, taxonomy, etc.), may yet be able to 
follow me along the path of analytical proof, and attempt to 
upset the conclusion as to the common origin of all species 
of all Calcareous Sponges which I have given in my Mono- 
graph. I must, however, repeat that this conclusion is 
based on the most minute investigation of an extraordinarily 
rich mass of material, — that it is securely established by 
thousands of the most careful microscopical observations, 
measurements, and comparisons of every single part, and 
that thousands of collected microscopic preparations render, 
at any moment, the most searching criticism of my results 
confirmatory of their correctness. One may hope, then, that 
opponents will endeavour to confront me on the ground of 
this " exact empiricism," instead of trying to damn my 
" nature-philosophical speculations." One may hope that 
they will endeavour to bring forward some evidence to 
show that the latter do not follow as the legitimate conse- 
quences of the former. May they, however, spare me the 
empty — though by even respectable naturalists oft-repeated 
— phrase, that the monistic nature-philosophy, as expounded 


in the "General Morphology," and in the "History of 
Creation," is wanting in actual proofs. The proofs are 
there. Of course those who turn their eyes away from 
them will not see them. Precisely that "exact " form of 
analytical proof which the opponents of the descent theory 
demand is to be found, by anybody who wishes to find it, 
in the " Monograph of the Calcareous Sponges." 

Eknst Heineich Haeckel. 

Jena, June 24-th, 1873. 


Feeling sure that such a book as Professor Haeckel's 
" Schopfungsgeschichte " would do a great deal of good, if 
placed in the hands of the English reading public, and of 
commencing students of Natural History, I gladly under- 
took to revise for the publishers the present translation, 
which was made by a young lady. I have not attempted 
to escape a difficulty by ignoring the German names made 
use of by Professor Haeckel for classes, orders, and genera, 
but have adopted English equivalents. I do not submit 
these names as a maturely considered English nomenclature, 
they appear here simply as necessary parts of a close ren- 
dering of the German work. I do, however, hold that some 
such series of English terms is both possible and useful, and 
do not doubt — in spite of the pretended hostility of the 
genius of our language, and the curious sentimental objec- 
tion that English names are unscientific — that we shall 
before long make use of plain English in speaking of the 
various groups of plants and animals — much to the gain of 
the larger public, and without detriment to the latinized 
nomenclature established for the purposes of the professional 

E. R L. 

Oxford, October, 1874. 




General Importance and Essential Natnre of the Theory of Descent as re. 
formed by Darwin. — Its Special Importance to Biology (Zoology and 
Botany). — Its Special Importance to the History of the Natural Develop- 
ment of the Human Pace. — The Theory of Descent as the Non-Miraculous 
History of Creation. — Idea of Creation. — Knowledge and Belief. — His- 
tory of Creation and History of Development.- — The Connection between 
the History of Individual and Palaeontological Development. — The 
Theory of Purposelessness, or the Science of Budimentary Organs. — 
Useless and Superfluous Arrangements in Organisms. — Contrast between 
the two entirely opposed Views of Nature : the Monistic (mechanical, 
causal) and the Dualistic (teleological, vital). — Proof of the former by 
the Theory of Descent. — Unity of Organic and Inorganic Nature, and 
the Identity of the Active Causes in both. — The Importance of the 
Theory of Descent to the Monistic Conception of all Nature. 

The intellectual movement to which the impulse was given, 
thirteen years ago, by the English naturalist, Charles 
Darwin, in his celebrated work, " On the Origin of 
Species," 1 has, within this short period, assumed dimen- 
sions which cannot but excite the most universal interest. It 
is true the scientific theory set forth in that work, which is 
commonly called briefly Darwinism, is only a small fragment 
of a far more comprehensive doctrine — a part of the universal 
VOL. L *)<? B 


Theory of Development, which embraces in its vast range 
the whole domain of human knowledge. 

But the manner in which Darwin has firmly established 
the latter by the former is so convincing, and the direction 
which has been given by the unavoidable conclusions of 
that theory to all our views of the universe, must appear to 
every thinking man of such deep significance, that its 
general importance cannot be over estimated. There is no 
doubt that this immense extension of our intellectual 
horizon must be looked upon as by far the most important, 
and rich in results, among all the numerous and grand 
advances which natural science has made in our day. 

When our century, with justice, is called the age of 
natural science, when we look with pride upon the im- 
mensely important progress made in all its branches, we 
are generally in the habit of thinking more of immediate 
practical results, and less of the extension of our general 
knowledge of nature. We call to mind the complete reform, 
so infinitely rich in consequences to human intercourse, 
which has been effected by the development of machinery, 
by railways, steamships, telegraphs, and other inventions 
of physics. Or we think of the enormous influence which 
chemistry has brought to bear upon medicine, agriculture, 
and upon all arts and trades. 

But much as we may value this influence of modern 
science upon practical life, still it must, estimated from a 
higher and more general point of view, stand most assuredly 
below the enormous influence which the theoretical progress 
of modern science will have on the entire range of human 
knowledge, on our conception of the universe, and on the 
perfecting of man's culture. 


Think of the immense revolutions in all our theoretical 
views which we owe to the general application of the 
microscope. Think of the cell theory, which explains the 
apparent unity of the human organism as the combined 
result of the union of a mass of elementary vital units. Or 
consider the immense extension of our theoretical horizon 
which we owe to spectral analysis and to the mechanical 
theory of heat. But among all these wonderful theoretical 
advances, the theory wrought out by Darwin occupies by 
far the highest rank. 

Every one of my readers has heard of the name of Dar- 
win. But most persons have probably only an imperfect 
idea of the real value of his theory. If a reader estimates 
as of equal value all that has been written upon Darwin's 
memorable work since its appearance, the value of the 
theory will appear very doubtful to him, supposing that 
he has not been engaged in the organic natural sciences, 
and has not penetrated into the inner secrets of zoology 
and botany. The criticisms of it are so full of contradic- 
tions, and for the most part so defective, that we ought not 
to be at all astonished that even now, after the lapse of 
thirteen years since the appearance of Darwin's work, it has 
not gained half that importance which is justly due to it, 
and which sooner or later it certainly will attain. 

Most of the innumerable writings which have been pub- 
lished during these years, both for and against Darwinism, 
are the productions of persons who are entirely wanting in 
the necessary amount of biological, and especially of zoolo- 
gical, knowledge. Although almost all of the more celebrated 
naturalists of the present day are adherents of the theory, 
yet only a few of them have endeavoured to procure its 


acceptance and recognition in larger circles. Hence the 
odd contradictions and the strange opinions which may still 
he heard everywhere ahont Darwinism. This is the reason 
which induces me to make Darwin's theory, and those further 
doctrines which are connected with it, the subject of these 
pages, which, I hope, will be generally intelligible. I hold 
it to be the duty of naturalists, not merely to meditate upon 
improvements and discoveries in the 'narrow circle to which 
their speciality confines them, not merely to pore over then- 
one study with love and care, but also to seek to make the 
important general results of it fruitful to the mass, and to 
assist in spreading the knowledge of physical science among 
the people. The highest triumph of the human mind, the 
true knowledge of the most general laws of nature, ought 
not to remain the private possession of a privileged class of 
savans, but ought to become the common property of all 

The theory which, through Darwin, has been placed at 
the head of all our knowledge of nature, is usually called the 
Doctrine of Filiation, or the Theory of Descent. Others term 
it the Transmutation Theory. Both designations are correct. 
For this doctrine affirms, that all organisms (viz. all species 
of animals, all species of plants, which have ever existed or 
still exist on the earth) are derived from one single, or from 
a few simple original forms, and that they have developed 
themselves from these in the natural course of a gradual 
change. Although this theory of development had already 
been brought forward and defended by several great natural- 
ists, and especially by Lamarck and Goethe, in the beginning 
of our century, still it was through Darwin, thirteen years 
ago, that it received its complete demonstration and causal 


foundation ; and this is the reason why now it is commonly 
and exclusively (though not quite correctly) designated as 
Darwin's Theory. 

The great and really inestimable value of the Theory of 
Descent appears in a different light, accordingly as we 
merely consider its more immediate connection with organic 
natural science, or its larger influence upon the whole range 
of man's knowledge of the universe. Organic natural 
science, or Biology, which as Zoology treats of animals, as 
Botany of plants, is completely reformed and founded anew 
by the Theory of Descent. For by this theory we are made 
acquainted with the active causes of organic forms, while up 
to the present time Zoology and Botany have simply been 
occupied with the facts of these forms. We may therefore 
also term the theory of descent a mechanical explanation of 
organic forms, or the science of the true causes of Organic 

As I cannot take for granted that my readers are all 
familiar with the terms " organic and inorganic nature," 
and as the contrast of both these natural bodies will, in 
future, occupy much of our attention, I must say a few 
words in explanation of them. We designate as Organisms, 
or Organic bodies, all living creatures »or animated bodies; 
therefore all plants and animals, man included ; for in them 
we can almost always prove a combination of various parts 
(instruments or organs) which work together for the purpose 
of producing the phenomena of life. Such a combination 
we do not find in Anorgana, or inorganic natural bodies — 
the so-called dead or inanimate bodies, such as minerals or 
stones, water, the atmospheric air, etc. Organisms always 
contain albuminous combinations of carbon in a semi-fluid 


condition of aggregation, which are always wanting in the 
Anorgana. Upon this important distinction rests the divi- 
sion of all natural history into two great and principal parts 
— Biology, or the science of Organisms (Zoology and Botany), 
and Anorganology, or the science of Anorgana (Mineralogy, 
Geology, Meteorology, etc.). 

The great value of the Theory of Descent in regard to 
Biology consists, as I have already remarked, in its explain- 
ing to us the origin of organic forms in a mechanical way, 
and pointing out their active causes. But however highly 
and justly this service of the Theory of Descent may be 
valued, yet it is almost eclipsed by the immense importance 
which a single necessary inference from it claims for itself 
alone. This necessary and unavoidable inference is the 
theory of the animal descent of the human race. 

The determination of the position of man in nature, and 
of his relations to the totality of things — this question of all 
questions for mankind, as Huxley justly calls it — is finally 
solved by the knowledge that man is descended from 
animals. In consequence of Darwin's reformed Theory of 
Descent, we are now in a position to establish scientifically 
the groundwork of a non-miraculous history of the de- 
velopment of the human race. All those who have defended 
Darwin's theory, as well as all its thoughtful opponents, have 
acknowledged that, as a matter of necessity, it follows from 
his theory that the human race, in the first place, must be 
traced to ape-like mammals, and further back to the lower 
vertebrate animals. 

It is true Darwin himself did not express at first this 
most important of all the inferences from his theory. In 
his work, " On the Origin of Species," not a word is found 


about the animal descent of man. The courageous but 
cautious naturalist was at that time purposely silent on the 
subject, for he anticipated that this most important of all 
the conclusions of the Theory of Descent was at the same 
time the greatest obstacle to its being generally accepted 
and acknowledged. Certain it is that Darwin's book would 
have created, from the beginning, even much more opposi- 
tion and offence, if this most important inference had at 
once been clearly expressed. It was not till twelve years 
later, in his work on " The Descent of Man, and Selection 
in Relation to Sex," that Darwin openly acknowledged that 
far-reaching conclusion, and expressly declared his entire 
agreement with those naturalists who had, in the mean- 
time, themselves formed that conclusion. Manifestly the 
effect of this conclusion is immense, and no science will be 
able to escape from the consequences. Anthropology, or the 
science of man, and consequently all philosophy, are thereby 
thoroughly reformed in all their various branches. 

It will be a later task in these pages to discuss this 
special point. I shall not treat of the theory of the animal 
descent of man till I have spoken of Darwin's theory, and 
its general foundation and importance. To express it in 
one word, that most important, but (to most men) at first 
repulsive, conclusion is nothing more than a special deduc- 
tion, which we must draw from the general inductive law 
of the descent theory (now firmly established), according to 
the stern commands of inexorable logic. 

Perhaps nothing will make the full meaning of the theory 
of descent clearer than calling it " the non-miraculous 
history of creation." I have therefore chosen that name 
for this work. It is, however, correct only in a certain 


sense, and it must be borne in mind that, strictly speaking, 
the expression "non-miraculous history of creation" contains 
a " contradictio in adjecto." 

In order to understand this, let us for a moment examine 
somewhat • more closely what we understand by creation. 
If we understand the creation to mean the coming into 
existence of a body by a creative power or force, we may 
then either think of the coming into existence of its sub- 
stance (corporeal matter), or of the coming into existence of 
its form (the corporeal form). 

Creation in the former sense, as the coming into existence 
of matter, does not concern us here at all. This process, if 
indeed it ever took place, is completely beyond human com- 
prehension, and can therefore never become a subject of 
scientific inquiry. Natural science teaches that matter is 
eternal and imperishable, for experience has never shown us 
that even the smallest particle of matter has come into 
existence or passed away. Where a natural body seems to 
disappear, as for example by burning, decaying, evaporation, 
etc., it merely changes its form, its physical composition or 
chemical combination. In like manner the coming; into 
existence of a natural body, for example, of a crystal, a 
fungus, an infusorium, depends merely upon the different 
particles, which had before existed in a certain form or com- 
bination, assuming a new form or combination in conse- 
quence of changed conditions of existence. But never yet 
has an instance been observed of even the smallest particle 
of matter having vanished, or even of an atom being added 
to the already existing mass. Hence a naturalist can no 
more imagine the coming into existence of matter, than he 
can imagine its disappearance, and he therefore looks upon 


the existing quantity of matter in the universe as a given 
fact. If any person feels the necessity of conceiving the 
coming into existence of this matter as the work of a super- 
natural creative power, of the creative force of something 
outside of matter, we have nothing to say against it. But 
we must remark, that thereby not even the smallest advan- 
tage is gained for a scientific knowledge of nature. Such a 
conception of an immaterial force, which at the first creates 
matter, is an article of faith which has nothing whatever 
to do with human science. Where faith commences, science 
ends. Both these arts of the human mind must be strictly 
kept apart from each other. Faith has its origin in the 
poetic imagination ; knowledge, on the other hand, originates 
in the reasoning intelligence of man. Science has to pluck 
the blessed fruits from the tree of knowledge, unconcerned 
whether these conquests trench upon the poetical imagin- 
ings of faith or not. 

If, therefore, science makes the " history of creation " its 
highest, most difficult, and most comprehensive problem, it 
must accept as its idea of creation the second explanation 
of the word, viz. the coming into being of the form of 
natural bodies. In this way geology, which tries to in- 
vestigate the origin of the inorganic surface of the earth as 
it now appears, and the manifold historical changes in the 
form of the solid crust of the earth, may be called the 
history of the creation of the earth. In like manner, the 
history of the development of animals and plants, which 
investigates the origin of living forms, and the manifold 
historical changes in animal and vegetable forms, may be 
termed the history of the creation of organisms. As, how- 
ever, in the idea of creation, although used in this sense, the 


unscientific idea of a creator existing outside of matter, and 
changing it, may easily creep in, it will perhaps he better in 
future to substitute for it the more accurate term, develop- 

The great value which the History of Development pos- 
sesses for the scientific understanding of animal and vege- 
table forms, has now been generally acknowledged for many 
years, and without it it would be impossible to make any 
sure progress in organic morphology, or the theory of forms. 
But by the history of development, only one part of this 
science has generally been understood, namely, that of 
organic individuals, usually called Embryology, but more 
correctly and comprehensively, Ontogeny. But, besides this, 
there is another history of development of organic species, 
genera, and tribes (phyla), which has the most important 
relations to the former. 

The subject of this is furnished to us by the science of 
petrifactions, or palaeontology, which shows us that each 
tribe of animals and plants, during different periods of the 
earth's history, has been represented by a series of entirely 
different genera and species. Thus, for example, the tribe 
of vertebrated animals was represented by classes of fish, 
amphibious animals, reptiles, birds, and mammals, and each 
of these groups, at different periods, by quite different kinds. 
This palseontological history of the development of organ- 
isms, which we may term Phylogeny, stands in the most 
important and remarkable relation to the other branch of 
organic history of development, I mean that of individuals, 
or Ontogeny. On the whole, the one runs paraUel to the 
other. In fact, the history of individual development, or 
Ontogeny, is a short and quick recapitulation of palseonto- 


logical development, or Phylogeny, dependent on the laws 
of Inheritance and Adaptation. 

As I shall have, later, to explain this most interesting and 
important coincidence more fully, I shall not dwell further 
upon it here, and merely call attention to the fact that it 
can only be explained and its causes understood by the 
Theory of Descent, while without that theory it remains 
completely incomprehensible and inexplicable. The Theory 
of Descent in the same way shows us why individual animals 
and plants must develop at all, and why they do not come 
into life at once in a perfect and developed state. No super- 
natural history of creation can in any way explain to us 
the great mystery of organic development. To this most 
weighty question, as well as to all other biological ques- 
tions, the Theory of Descent gives us perfectly satisfactory 
answers — and always answers which refer to purely me- 
chanical causes, and point to purely physico-chemical forces 
as the causes of phenomena which we were formerly accus- 
tomed to ascribe to the direct action of supernatural, 
creative forces. Hence, by our theory the mystic veil of 
the miraculous and supernatural, which has hitherto been 
allowed to hide the complicated phenomena of this branch 
of natural knowledge, is removed. All the departments of 
Botany and Zoology, and especially the most important por- 
tion of the latter, Anthropology, become reasonable. The 
dimming mirage of mythological fiction can no longer 
exist in the clear sunlight of scientific knowledge. 

Of special interest among general biological phenomena 
are those which are quite irreconcilable with the usual 
supposition, that every organism is the product of a creative 
power, acting for a definite object. Nothing in this respect 


caused the earlier naturalists greater difficulty than the 
explanation of the so-called " rudimentary organs,"— those 
parts in animal and vegetable bodies which really have no 
function, which have no physiological importance, and yet 
exist in form. These parts deserve the most careful atten- 
tion, although most unscientific men know little or nothing 
about them. Almost every organism, almost every animal 
and plant possesses, besides the obviously useful arrange- 
ments of its organization, other arrangements the purpose 
of which it is utterly impossible to make out. 

Examples of this are found everywhere. In the embryos 
of many ruminating animals — among others, in our common 
cattle — fore-teeth, or incisors, are placed in the mid-bone of 
the upper jaw, which never fully develop, and therefore 
serve no purpose. The embryos of many whales- — which 
afterwards possess the well-known whalebone instead of 
teeth, yet have before they are born, and while they take no 
nourishment, teeth in their jaws, which set of teeth never 
comes into use. Moreover, most of the higher animals pos- 
sess muscles which are never employed ; even man has such 
rudimentary muscles. Most of us are incapable of moving 
our ears as we wish, although the muscles for this move- 
ment exist, and although individual persons who have 
taken the trouble to exercise these muscles do succeed in 
moving their ears. It is still possible, by special exercise, 
by the persevering influence of the will upon the nervous 
system, to reanimate the almost extinct activity in the 
existing but imperfect organs, which are on the road to 
complete disappearance. On the other hand, we can no 
longer do this with another set of small rudimentary 
muscles, which still exist in the cartilage of the outer ear, 


but which are always perfectly inactive. Our long-eared 
ancestors of the tertiary period — apes, semi-apes, and 
pouched animals, like most other mammals, moved their 
large ear-flaps freely and actively; their muscles were much 
more strongly developed and of great importance. In a 
similar way, many varieties of dogs and rabbits, under the 
influence of civilized life, have left off " pricking up " their 
ears, and thereby have acquired imperfect auricular muscles 
and loose-hanging ears, although their wild ancestors moved 
their stiff ears in many ways. 

Man has also these rudimentary organs on other parts of 
his body ; they are of no importance to life, and never per- 
form any function. One of the most remarkable, although 
the smallest organ of this kind, is the little crescent-like fold, 
the so-called "plica semilunaris," which we have in the 
inner corner of the eye, near the root of the nose. This in- 
significant fold of skin, which is quite useless to our eye, 
is the imperfect remnant of a third inner eyelid which, 
besides the upper and under eyelid, is highly developed in 
other mammals, and in birds and reptiles. Even our very 
remote ancestors of the Silurian period, the Primitive Fishes, 
seem to have possessed this third eyelid, the so-called nicti- 
tating membrane. For many of their nearest kin, who still 
exist in our day but little changed in form, viz. many 
sharks, possess a very strong nictitating membrane, which 
they can draw right across the whole eyeball, from the inner 
corner of the eye. 

Eyes which do not see form the most striking example of 
rudimentary organs. These are found in very many animals, 
which live in the dark, as in caves or underground. Their 
eyes often exist in a well-developed condition, but they are 


covered by membrane, so that no ray of light can enter, 
and they can never see. Such eyes, without the function 
of sight, are found in several species of moles and mice which 
live underground, in serpents and lizards, in amphibious 
animals (Proteus, Csecilia), and in fishes ; also in numerous 
invertebrate animals, which pass their lives in the dark, 
as do many beetles, crabs, snails, worms, etc. 

An abundance of the most interesting examples of rudi- 
mentary organs is furnished by Comparative Osteology, or 
the study of the skeletons of vertebrate animals, one of the 
most attractive branches of Comparative Anatomy. In most 
of the vertebrate animals we find two pairs of limbs on the 
body, a pair of fore-legs and a pair of hind-legs. Very often, 
however, one or the other pair is imperfect; it is seldom 
that both are, as in the case of serpents and some varieties of 
eel-like fish. But some serpents, viz. the giant serpents (Boa, 
Python), have still in the hinder portion of the body some 
useless little bones, which are the remains of lost hind-legs. 

In like manner the mammals of the whale tribe (Cetacea), 
which have only fore-legs fully developed (breast-fins ), have 
further back in their body another pair of utterly superfluous 
bones, which are remnants of undeveloped hind-legs. The 
same thing occurs in many genuine fishes, in which the 
hind-legs have in like manner been lost. 

Again, in our slow- worm (Anguis), and in some other 
lizards, no fore-legs exist, although they have a perfect 
shoulder apparatus within their bodies, which should serve 
as a means of affixing the legs. Moreover, in various ver- 
tebrate animals, the single bones of both pairs of legs are 
found in all the different stages of imperfection, and often 
the degenerate bones and those muscles belonging to them 


are partially preserved, without their being able in any way 
to perform any function. The instrument is still there, but 
it can no longer play. 

Moreover, we can, almost as generally, find rudimentary 
organs in the blossoms of plants, inasmuch as one part or 
another of the male organs of propagation — the stamen and 
anther, or of the female organs of propagation — the style, 
germ, etc. — is more or less imperfect or abortive. Among 
these we can trace, in various closely connected species of 
plants, the organ in all stages of degeneration. Thus, for 
example, the great natural family of lip-blossomed plants 
(Labiatce), to which the balm, peppermint, marjoram, ground- 
ivy, thyme, etc., belong, are distinguished by the fact that 
their mouth-like, two-lipped flower contains two long and 
two short stamens. But in many exceptional plants of this 
family, e. g. in different species of sage, and in the rosemary, 
only one pair of stamens is developed; the other pair is more 
or less imperfect, or has quite disappeared. Sometimes 
stamens exist, but without the anthers, so that they are 
utterly useless. Less frequently the rudiment or imperfect 
remnant of a fifth stamen is found, physiologically (for the 
functions of life) quite useless, but morphologically (for the 
knowledge of the form and of the natural relationship) 
a most valuable organ. In my " General Morphology 
of Organisms," 4 in the chapter on " Purposelessness, or 
Dysteleology," I have given a great number of other 
examples (Gen. Morph. ii. 226). 

No biological phenomenon has perhaps ever placed 
zoologists or botanists in greater embarrassment than these 
rudimentary or abortive organs. They are instruments 
without employment, parts of the body which exist without 


performing any service — adapted for a purpose, but without 
in reality fulfilling that purpose. When we consider the 
attempts which the earlier naturalists have made in order 
to explain this mystery, we can scarcely help smiling at the 
strange ideas to which they were led. Being unable to find 
a true explanation, they came, for example, to the conclu- 
sion that the Creator had placed these organs there "for the 
sake of symmetry," or they believed that it had appeared 
unwise and unsuitable to the Creator (seeing that their 
nearest kin did possess such organs) that these organs 
should be completely wanting in creatures, where they 
are incapable of performing a function, and where it 
cannot be otherwise from the special mode of life. In 
compensation for the non-existing function, he had at least 
furnished them with the outward but empty form ; nearly 
in the same manner as civil officers, in uniform, are furnished 
with an innocent sword, which is never drawn from the 
scabbard. I scarcely believe, however, that any of my 
readers will be content with such an explanation. 

Now, it is precisely this widely spread and mysterious 
phenomenon of rudimentary organs, in regard to which all 
other attempts at explanation fail, which is perfectly ex- 
plained, and indeed in the simplest and clearest way, by 
Darwin's Theory of Inheritance and Adaptation. We can 
trace the important laws of inheritance and adaptation in 
the domestic animals which we breed, and the plants which 
we cultivate ; and a series of such laws of inheritance have 
already been established. Without going further into this 
at present, I will only remark that some of them perfectly 
explain, in a mechanical way, the coming into existence of 
rudimentary organs, so that we must look upon the appear- 


ance of such structures as au entirely natural process, arising 
from the disuse of the organs. 

By adaptation to special conditions of life, the formerly 
active and really .working organs have gradually ceased 
to be used or employed. In consequence of their not being 
exercised they have become more and more imperfect, but 
in spite of this have always been handed down from one 
generation to another by inheritance, until at last they 
vanish partially or entirely. Now, if we admit that all 
the vertebrate animals mentioned above are derived from 
one common ancestor, possessing two seeing eyes and two 
well developed pairs of legs, the different stages of suppres- 
sion and degeneration of these organs are easily accounted 
for in such of the descendants as could no longer use them. 
In like manner the various stages of suppression of the 
stamens, originally existing to the number of five (in the 
flower-bud), among the Labiatse is explained, if we admit 
that all the plants of this family sprung from one common 
ancestor, provided with five stamens. 

I have here spoken somewhat fully of the phenomena of 
rudimentary organs, because they are of the utmost general 
importance, and because they lead us to the great, general, 
and fundamental questions in philosophy and natural 
science, for the solution of which the Theory of Descent 
has now become the indispensable guide. As soon, in fact, 
as, according to this theory, we acknowledge the exclusive 
activity of physico-chemical causes in living (organic) 
bodies, as well as in so-called inanimate (inorganic) nature, 
we concede exclusive dominion to that view of the uni- 
verse, which we may designate as the mechanical, and 
which is opposed to the ideological conception. If we 

VOL. I. - C 


compare all the ideas of the universe prevalent among 
different nations at different times, we can divide them 
all into two sharply contrasted groups — a causal or me- 
chanical, and a ideological or vitalistic. The latter has pre- 
vailed generally in Biology until now, and accordingly the 
animal and vegetable kingdoms have been considered as 
the products of a creative power, acting for a definite pur- 
pose. In the contemplation of every organism the unavoid- 
able conviction seemed to press itself upon us, that such a 
wonderful machine, so complicated an apparatus for motion 
as exists in the organism, could only be produced by a 
power analogous to, but infinitely more perfect than, the 
power of man in the construction of his machines. 

However sublime the former idea of a Creator, and his 
creative power, may have been ; however much it may be 
attempted to divest it of all human analogy, yet in the end 
this analogy still remains unavoidable and necessary in the 
teleological conception of nature. In reality the Creator 
must himself be conceived of as an organism, that is, as a 
being who, analogous to man, even though in an infinitely 
more perfect form, reflects on his constructive power, lays 
down a plan of his mechanisms, and then, by the application 
of suitable materials, makes them answer their purpose. 
Such conceptions necessarily suffer from the fundamental 
error of anthropomorphism, or man-hkening. In such a 
view, however exalted the Creator may be imagined, we 
assign to him the human attributes of designing a plan, 
and therefrom suitably constructing the organism. This is, 
in fact, quite clearly expressed in that view which is most 
sharply opposed to Darwin's theory, and which has found 
among naturalists its most distinguished representative in 


Agassiz. His celebrated work, " An Essay on Classifica- 
tion," 5 which is entirely opposed to Darwin's, and appeared 
almost at the same time, has elaborated quite consistently, 
and to the utmost extent, these anthropomorphic conceptions 
of the Creator. 

I maintain with regard to the much-talked-of "purpose 
in nature," that it really has no existence but for those 
persons who observe phenomena in animals and plants in 
the most superficial manner. Without going more deeply 
into the matter, we can see at once that the rudimentary 
organs are a formidable obstacle to this theory. And, indeed, 
every one who makes a really close study of the organization 
and mode of life of the various animals and plants, and 
becomes familiar with the reciprocity or inter-action of the 
phenomena of fife, and the so-called " economy of nature," 
must necessarily come to the conclusion that this 
" purposiveness " no more exists than the much-talked-of 
" beneficence " of the Creator. These optimistic views have, 
unfortunately, as little real foundation as the favourite 
phrase, the " moral order of the universe," which is illustrated 
in an ironical way by the history of all nations. The 
dominion of the " moral " popes, and their pious inquisition, 
in the mediaeval times, is not less significant of this than 
the present prevailing militarism, with its " moral " 
apparatus of needle-guns and other refined instruments of 

If we contemplate the common life and the mutual rela- 
tions between plants and animals (man included), we shall 
find everywhere, and at all times, the very opposite of that 
kindly and peaceful social life which the goodness of the 
Creator ought to have prepared for his creatures — we shall 


rather find everywhere a pitiless, most embittered Struggle 
of All against All. Nowhere irj nature, no matter where 
we turn our eyes, does that idyllic peace, celebrated by 
the poets, exist ; we find everywhere a struggle and a 
striving to annihilate neighbours and competitors. Passion 
and selfishness — conscious or unconscious — is everywhere 
the motive force of life. The well-known words of the 
German poet — 

" Die Welt ist vollkommen liberall 
Wo der Mensch nicht hinkommt mit seiner Qual." * 

are beautiful, but, unfortunately, not true. Man in this re- 
spect certainly forms no exception to the rest of the animal 
world. The remarks which we shall have to make on the 
theory of "Struggle for Existence " will sufficiently justify 
this assertion. It is, in fact, Darwin who has placed this 
important point, in its high and general significance, very 
clearly before our eyes, and the chapter in his theory 
which he himself calls " Struggle for Existence " is one of 
the most important parts of it. 

Whilst, then, we emphatically oppose the vital or 
teleological view of animate nature which presents animal 
and vegetable forms as the productions of a kind Creator, 
acting for a definite purpose, or of a creative, natural 
force acting for a definite purpose, we must, on the other 
hand, decidedly adopt that view of the universe which is 
called the mechanical or causal. It may also be called the 
monistic, or single-principle theory, as opposed to the two- 
fold principle, or dualistic theory, which is necessarily 
implied in the teleological conception of the universe. The 

* The world is perfect save where Man 
Comes in with his strife. 


mechanical view of nature has for many years been so 
firmly established in certain domains of natural science, that 
it is here unnecessary to say much about it. It no longer 
occurs to physicists, chemists, mineralogists, or astronomers, 
to seek to find in the phenomena which continually appear 
before them in their scientific domain the action of a Creator 
acting for a definite purpose. They universally, and with- 
out hesitation, look upon the phenomena which appear in 
their different departments of study as the necessary and 
invariable effects of physical and chemical forces which are 
inherent in matter. Thus far their view is purely material- 
istic, in a certain sense of that " word of many meanings." 

When a physicist traces the phenomena of motion in elec- 
tricity or magnetism, the fall of a heavy body, or the 
undulations in the waves of light, he never, in the whole 
course of his research, thinks of looking for the interference 
of a supernatural power. In this respect, Biology, as the 
science of so-called " animated " natural bodies, was formerly 
placed in sharp opposition to the above-mentioned inorganic 
natural sciences (Anorganology). It is true modern Physi- 
ology, the science of the phenomena of motion in animals 
and plants, has completely adopted the mechanical view ; but 
Morphology, the science of the forms of animals and plants, 
has not been affected at all by it. Morphologists, in spite of 
the position of physiology, have continued, as before, in oppo- 
sition to the mechanical view of functions, to look upon the 
forms of animals and plants as something which cannot be 
at all explained mechanically, but which must owe its origin 
necessarily to a higher, supernatural creative power, acting 
for a definite purpose. 

In this general view it is quite indifferent whether the 


creative power be worshipped as a personal god, or whether 
it he termed the power of life (vis vitalis), or final cause 
(causa finalis). In any case, to express it in one word, its 
supporters have recourse to a miracle for an explanation. 
They throw themselves into the arms of a poetic faith, 
which as such can have no value in the domain of scientific 

All that was done before Darwin, to establish a natural 
mechanical conception of the origin of animals and plants, 
has been in vain, and until his time no theory gained a 
general recognition. Darwin's theory first succeeded in 
doing this, and thus has rendered an immense service. For 
the idea of the unity of organic and inorganic nature 
is now firmly established; and that branch of natural 
science which had longest and most obstinately opposed 
mechanical conception and explanation, viz. the science of 
the structure of animate forms, is launched on to identically 
the same road towards perfection as that along which all the 
rest of the natural sciences are travelling. The unity of all 
natural phenomena is by Darwin's theory finally established 

This unity of all nature, the animating of all matter, the 
inseparability of mental power and corporeal substance, 
Goethe has asserted in the words : " Matter can never exist 
and be active without mind, nor can mind without matter." 
These first principles of the mechanical conception of the 
universe have been taught by the great monistic philosophers 
of all ages. Even Democritus of Abdera, the immortal 
founder of the Atomic theory, clearly expressed them about 
500 years before Christ; but the great Dominican friar, 
Giordano Bruno, did so even more explicitly. For this he 
was burnt at the stake, by the Christian inquisition in 


Rome, on the 17th of Feb., 1600, on the same day on 
which, 36 years befwe, Galileo, his great fellow-countryman 
and fellow-worker, was horn. Such men, who live and die 
for a great idea, are usually stigmatized as " materialists " ; 
hut their opponents, whose arguments were torture and the 
stake, are praised as " spiritualists." 

By the Theory of Descent we are for the first time enabled 
to conceive of the unity of nature in such a manner that 
a mechanico-causal explanation of even the most intricate 
organic phenomena, for example, the origin and structure 
of the organs of sense, is no more difficult (in a general 
way) than is the mechanical explanation of any physical 
process ; as, for example, earthquakes, the courses of the wind, 
or the currents of the ocean. We thus arrive at the 
extremely important conviction that all natural bodies 
which are known to us are equally animated, that the 
distinction which has been made between animate and 
inanimate bodies does not exist. When a stone is thrown 
into the air, and falls to earth according to definite laws, or 
when in a solution of salt a crystal is formed, the phenomenon 
is neither more nor less a mechanical manifestation of life 
than the growth and flowering of plants, than the propaga- 
tion of animals or the activity of their senses, than the 
perception or the formation of thought in man. This 
final triumph of the monistic conception of nature consti- 
tutes the highest and most general merit of the Theory of 
Descent, as reformed by Darwin. 





The Theory of Descent, or Doctrine of Filiation, as the Monistic Explana- 
tion of Organic Natural Phenomena. — Its Comparison with Newton's 
Theory of Gravitation. — Limits of Scientific Explanation and of Human 
Knowledge in general. — All Knowledge founded originally on Sensuous 
Experience, d, posteriori. — Transition of d posteriori knowledge, by In- 
heritance, into d priori knowledge. — Contrast between the Supernatural 
Hypotheses of the Creation according to Linnaeus, Cuvier, Agassiz, and 
the Natural Theories of Development according to Lamarck, Goethe, 
and Darwin. — Connection of the former with the Monistic (mechanical), 
of the latter with the Dualistic Conception of the Universe. — Monism 
and Materialism. — Scientific and Moral Materialism. — The History of 
Creation according to Moses. — Linnaeus as the Founder of the Systematic 
Description of Nature and Distinction of Species. —Linnaeus' Classifica- 
tion and Binary Nomenclature. — Meaning of Linnaeus' Idea of Species. 
— His History of Creation. — Linnaeus' view of the Origin of Species. 

The value which every scientific theory possesses is 
measured by the number and importance of the objects 
which can be explained by it, as well as by the simplicity 
and universality of the causes which are employed in it as 
grounds of explanation. On the one hand, the greater the 
number and the more important the meaning of the 
phenomena explained by the theory, and the simpler, on 
the other hand, and the more general the causes which the 
theory assigns as explanations, the greater is its scientific 


value, the more safely we are guided by it, and the more 
strongly are we bound to adopt it. 

Let us call to mind, for example, that theory which has 
ranked up to the present time as the greatest achievement 
of the human mind — the Theory of Gravitation, which 
Newton, two hundred years ago, established in his Mathe- 
matical Principles of Natural Philosophy. Here we find 
that the object to be explained is as large as one can well 
imacine. He undertook to reduce the phenomena of the 
motion of the planets, and the structure of the universe, to 
mathematical laws. As the most simple cause of these in- 
tricate phenomena of motion, Newton established the law 
of weight or attraction, the same law which is the cause of 
the fall of bodies, of adhesion, cohesion, and many other 

If we apply the same standard of valuation to Darwin's 
theory, we must arrive at the conclusion that this theory, 
also, is one of the greatest achievements of the human mind, 
and that it may be placed quite on a level with Newton's 
Theory of Gravitation. Perhaps this opinion will seem a 
little exaggerated, or at any rate very bold, but I hope in 
the course of this treatise to convince the reader that this 
estimate is not too high. In the preceding chapter, some 
of the most important and most general phenomena in 
organic nature, which have been explained by Darwin's 
theory, have been named. Among them are the varia- 
tions in form which accompany the individual development 
of organisms, most varied and complicated phenomena, 
which until now presented the greatest difficulties in the 
way of mechanical explanation, that is, in the tracing of 
them to active causes. We have mentioned the rudimen- 


tary organs, those exceedingly remarkable structures in 
animals and plants which have no object and refute every 
teleological explanation seeking for the final purpose of the 
organism. A great number of other phenomena might have 
been mentioned, which are no less important, and are ex- 
plained in the simplest manner by Darwin's reformed 
Theory of Descent. For the present I will only mention 
the phenomena presented to us by the geographical distri- 
bution of animals and plants on the surface of our planet, 
as well as the geological distribution of the extinct and 
petrified organisms in the different strata of the earth's 
crust. These important palseontological and geographical 
phenomena, which were formerly only known to us as facts, 
are now traced to their active causes by the Theory of 

The same statement applies further to all the general laws 
of Comparative Anatomy, especially to the great law of 
division of labour or separation (polymorphism, or dif- 
ferentiation), a law which determines the form or structure 
of human society, as well as the organization of individual 
animals and plants. It is this law which necessitates an 
ever increasing variety, as well as a progressive develop- 
ment of organic forms. This law of the division of labour 
has, up to the present time, been only recognized as a fact, 
and it, bike the law of progressive development, or the law 
of progress which we perceive active everywhere in the 
history of nations (as also in that of animals and plants), is 
explained by Darwin's Doctrine of Descent. Then, if we 
turn our attention to the great whole of organic nature, if 
we compare all the individual groups of phenomena of this 
immense domain of life, it cannot fail to appear, in the light 


of the Doctrine of Descent, no longer as the ingeniously 
designed work of a Creator building up according to a 
definite purpose, but as the necessary consequence of active 
causes, which are inherent in the chemical combination of 
matter itself, and in its physical properties. 

In fact, we can most positively assert, and I shall justify 
this assertion in the course of these pages, that by the Doc- 
trine of Filiation, or Descent, we are enabled for the first time 
to reduce all organic phenomena to a single law, and to dis- 
cover a single active cause for the infinitely intricate 
mechanism of the whole of this rich world of phenomena. 
In this respect, Darwin's theory stands quite on a level with 
Newton's Theory of Gravitation ; indeed, it even rises higher 
than Newton's theory ! 

The grounds of explanation are equally simple in the two 
theories. In explaining this most intricate world of phe- 
nomena, Darwin does not make use of new or hitherto 
unknown properties of matter, nor does he, as one might 
suppose, make use of discoveries of new combinations 
of matter or of new forces of organization ; but it is 
simply by extremely ingenious combination, by the syn- 
thetic comprehension, and by the thoughtful compa- 
rison of a number of well-known facts, that Darwin has 
solved the "holy mystery " of the living world of forms. The 
consideration of the interchanging relations which exist 
between two general properties of organisms, viz. Inherit- 
ance and Adaptation, is what has here been of the first 
importance. Merely by considering the relations between 
these two vital actions or physiological functions of organ- 
isms, also further by considering the reciprocal inter-action 
which all animals and plants, living in one and the same 


place, necessarily exert on one another — solely by the correct 
estimate of these simple facts, and by skilfully combining 
them, Darwin has succeeded in finding the true active 
causes (causae efficientes) of the immensely intricate world 
of forms in organic nature. 

In any case we are in duty bound to accept this theory 
till a better one be found, which will undertake to explain 
the same amount of facts in an equally simple manner. 
Until now we have been in utter want of such a theory. 
The fundamental idea that all different animal and vege- 
table forms must be descended from a few or even from one 
single, most simple primary form, was indeed not new. This 
idea was long since distinctly formulated — first by the great 
Lamarck, at the beginning of our century. But Lamarck 
in reality only expressed the hypothesis of the Doctrine of 
Filiation, without establishing it by an explanation of the 
active causes. And it is just the demonstration of these 
causes which marks the extraordinary progress which 
Darwin's theory has made beyond that of Lamarck. In 
the physiological properties of Inheritance and Adaptation 
of organic matter, Darwin discovered the true cause of the 
genealogical relationship of organisms. It was not possible 
for the genius of Lamarck in his day to command that 
colossal material of biological facts which has been collected 
by the patient zoological and botanical investigations of the 
last fifty years, and which has been used by Darwin as an 
overpowering apparatus of evidence. 

Darwin's theory is therefore not what his opponents fre- 
quently represent it as being — an unwarranted hypothesis 
taken up at random. It is not for zoologists or botanists to 
accept or reject this as an explanatory theory, as they 


please ; they are rather compelled and obliged to accept 
it, according to the general principle observed in all natural 
sciences, that we must accept and retain for the explanation 
of phenomena any theory which, though it has only a 
feeble basis, is compatible with the actual facts — until it is 
replaced by a better one. If we do not adopt it, we re- 
nounce a scientific explanation of phenomena, and this is, 
in fact, the position which many biologists still maintain. 
They look upon the whole domain of animate nature as a 
perfect mystery, and upon the origin of animals and plants, 
the phenomena of their development and affinities, as quite 
inexplicable and miraculous ; in fact, they will not allow that 
there can be a true understanding of them. 

Those opponents of Darwin who do not exactly wish to 
renounce a scientific explanation are in the habit of saying, 
" Darwin's theory of the common origin of the different 
species is only one hypothesis; we oppose to it another, 
the hypothesis that the individual animal and vegetable 
species have not developed one from another by descent, 
but that they have come into existence independently of 
one another, by a still undiscovered law of nature." But as 
long as it is not shown how this coming into existence is 
to be conceived of, and what that " law of nature " is — as 
long as not even -probable grounds of explanation can be 
brought forward to account for the independent coming 
into existence of animal and vegetable species, so long this 
counter-hypothesis is in fact no hypothesis, but an empty 
unmeaning phrase. Darwin's theory ought, moreover, not 
to be called an hypothesis. For a scientific hypothesis 
is a supposition, postulating the existence of unknown 
properties or motional phenomena of natural bodies, which 


properties have not as yet been observed by the experience 
of the senses. But Darwin's theory does not assume such 
unknown conditions ; it is based upon general properties 
of organisms that have long been recognized, and — as has 
been remarked — it is the exceedingly ingenious and com- 
prehensive combination of a number of phenomena which 
had hitherto stood isolated, which gives the theory its 
extraordinarily great and intrinsic value. By it we are 
for the first time in a position to demonstrate an active 
cause for all the known morphological phenomena in the 
animal and vegetable kingdoms ; and, in fact, this cause is 
always one and the same, viz. the alternate action of Adap- 
tation and Inheritance, therefore a physiological, that is, a 
physico-chemical or mechanical, relationship. For these 
reasons the acceptance of the Doctrine of Filiation, as 
mechanically established by Darwin, is a binding and un- 
avoidable necessity for the whole domain of zoology and 

As, therefore, in my opinion the immense importance of 
Darwin's theory lies in the fact that it has mechanically 
explained those organic 'phenomena of forms which had 
hitherto been unexplained, it is perhaps necessary that I 
should here say a few words about the different ideas con- 
nected with the word " explanation." It is very frequently 
said, in opposition to Darwin's theory, that it does indeed 
explain those phenomena by Inheritance and Adaptation, 
but that it does not at the same time explain those pro- 
perties of organic matter, and that therefore we do not 
arrive at first causes. This objection is quite correct, but it 
applies equally to all explanations of phenomena. We no- 
where arrive at a knowledge of first causes. The origin of 


every simple salt crystal, which we obtain by evaporating 
its mother liquor, is no less mysterious to us, as far as con- 
cerns its first cause, and in itself no less incomprehensible 
than the origin of every animal which is developed out 
of a simple cell. In explaining the most simple physical or 
chemical phenomena, as the falling of a stone, or the forma- 
tion of a chemical combination, we arrive, by discovering 
and establishing the active causes — for example, the gravi- 
tation or the chemical affinity — at other remoter phenomena, 
which in themselves are mysterious. This arises from the 
limitation or relativity of our powers of understanding. 
We must not forget that human knowledge is absolutely 
limited, and possesses only a relative extension. It is, in 
its essence, limited by the very nature of our senses and of 
our brains. 

All knowledge springs from sensuous perceptions. In 
opposition to this statement, the innate, a priori know- 
ledge of man may be brought up ; but we can see that the 
so-called a priori knowledge can by Darwin's theory be 
proved to have been acquired a posteriori, being based on 
experience as its first cause. Knowledge which is based 
originally upon purely empirical observations, and which is 
therefore a purely sensuous experience, but has then been 
transmitted from generation to generation by inheritance, 
appears in later generations as if it were independent, 
innate, and a priori. In our late animal ancestors, all our 
so-called " a priori knowledge " was originally acquired & 
posteriori, and only gradually became a priori by inherit- 
ance. It is based in the first instance upon experiences, 
and by the laws of Inheritance and Adaptation we can 
positively prove that knowledge a priori and knowledge a 


posteriori cannot rightly be placed in opposition, as is 
usually done. On the contrary, sensuous experience is 
the original source of all knowledge. For this reason alone, 
all our knowledge is limited, and we can never apprehend 
the first causes of any phenomena. The force of crystal- 
lization, the force of gravitation, and chemical affinity 
remain in themselves just as incomprehensible as do 
Adaptation and Inheritance. 

Seeing that Darwin's theory explains from a single point 
of view the totality of all those phenomena of which we 
have given a brief survey, that it demonstrates one and 
the same quality of the organism as the active cause in all 
cases, we must allow that it gives us for the present all 
that we can desire. Moreover, we have good reason to hope 
that at some future time we shall learn to explain the first 
causes at which Darwin has arrived, namely, the properties 
of Adaptation and Inheritance ; and that we shall succeed in 
discovering in the composition of albuminous matter certain 
molecular relations as the remoter, simpler causes of these 
phenomena. There is indeed no prospect of this in the 
immediate future, and we content ourselves for the present 
with the tracing back of organic phenomena to two 
mysterious properties, just as in the case of Newton's 
theory we are satisfied with tracing the planetary motions 
to the force of gravitation, which itself is likewise a mys- 
tery to us and not cognizable in itself. 

Before commencing our principal task, which is the care- 
ful discussion of the Doctrine of Descent, and the conse- 
quences that arise out of it, let us take an historical retro- 
spect of the most important and most widely spread of those 
views, which before Darwin men had elaborated concerning 


organic creation, and the coming into existence of the many 
animal and vegetable species. In doing this I have no inten- 
tion of entertaining the reader with a statement of all 
the innumerable stories about the creation which have 
been current among the different human species, races, or 
tribes. However interesting and gratifying this task would 
be, from an ethnographical point of view, as well as in a 
history of civilization, it would lead us here much too far 
from our subject. Besides, the great majority of all these 
legends about creation bear too clearly the stamp of arbi- 
trary fiction, and of a want of a close observance of nature, to 
be of interest in a scientific treatment of the history of crea- 
tion. I shall therefore only select the Mosaic history from 
among those that are not founded on scientific investigation, 
on account of the unparalleled influence which it has gained 
in the western civilized world ; and then I shall immedi- 
ately take up the scientific hypothesis about creation, which 
originated with Linnaeus as late as the commencement of 
last century. 

All the different conceptions which man has ever formed 
about the coming into existence of the different animal and 
vegetable species may conveniently be divided into two 
great contrasted groups — the natural and supernatural his- 
tories of creation. 

These two groups, on the whole, correspond with the two 
different principal forms of the human notions of the uni- 
verse which we have already contrasted as the monistic and 
the dualistic conception of nature. In the usual dualistic or 
teleological (vital) conception of the universe, organic nature 
is regarded as the purposely executed production of a Creator 
wcg'king according to a definite plan. Its adherents see in 

VOL. I. -i- D 


every individual species of animal and plant an " embodied 
creative thought," the material expression of a definite first 
cause (causa finalis) acting for a set purpose. They must 
necessarily assume supernatural (not mechanical) processes 
for the origin of organisms. With justice, we may therefore 
designate their scheme of the world's growth as the Super- 
natural History of Creation. Among all such teleological 
histories of creation, that of Moses has gained the greatest 
influence, since even so distinguished a naturalist as Lin- 
naeus has claimed admittance for it in Natural Science. 
Cuvier's and Agassiz's views of creation also belong to this 
group, as do in fact those of the great majority of both 
scientific and unscientific men. 

On the other hand, the theory of development earned out 
by Darwin, which we shall have to treat of here as the Non- 
miraculous or Natural History of Creation, and which has 
already been put forward by Goethe and Lamarck, must, 
if carried out logically, lead to the monistic or mechan- 
ical (causal) conception of the universe. In opposition to 
the dualistic or teleological conception of nature, our theory 
considers organic, as well as inorganic, bodies to be the neces- 
sary products of natural forces. It does not see in every in- 
dividual species of animal and plant the embodied thought 
of a personal Creator, but the expression for the time being 
of a mechanical process of development of matter, the ex- 
pression of a necessarily active cause, that is, of a mechanical 
cause (causa efficiens). Where teleological Dualism seeks 
the arbitrary thoughts of a capricious Creator in the miracles 
of creation, causal Monism finds in the process of develop- 
ment the necessary effects of eternal immutable laws of 


The Monism here maintained by us is often considered 
identical with Materialism. Now, as Darwinism, and in 
fact the whole theory of development, has been designated as 
" materialistic," I cannot avoid here at once guarding myself 
against this ambiguous word, and against the malice with 
which, in certain quarters, it is employed to stigmatize our 

By the word "Materialism," two completely different 
things are very frequently confounded and mixed up, which 
in reality have nothing whatever to do with each other, 
namely, scientific and moral materialism. Scientific mate- 
rialism, which is identical with ova- Monism, affirms in 
reality no more than that everything in the world goes on 
naturally — that every effect has its cause, and every cause its 
effect. It therefore assigns to causal law — that is, the law 
of a necessary connection between cause and effect — its 
place over the entire series of phenomena that can be 
known. At the same time, scientific materialism positively 
rejects every belief in the miraculous, and every conception, 
in whatever form it appears, of supernatural processes. 
Accordingly, nowhere in the whole domain of human know- 
ledge does it recognize real metaphysics, but throughout 
only physics ; through it the inseparable connection between 
matter, form, and force becomes self evident. This scientific 
materialism has long since been so universally acknowledged 
in the wide domain of inorganic science, in Physics and 
Chemistry, in Mineralogy and Geology, that no one now 
doubts its sole authority. But in Biology, or Organic science, 
the case is very different; here its value is still continually a 
matter of dispute in many quarters. There is, however, 
nothing else which can be set up against it, excepting the 


metaphysical spectre of a vital power, or empty theological 
dogma. If we can prove that all nature, so far as it can be 
known, is only one, that the same "great, eternal, iron 
laws" are active in the life of animals and plants, as in 
the growth of crystals and in the force of steam, we may 
with reason maintain the monistic or mechanical view 
of things throughout the domain of Biology — in Zoology and 
Botany — whether it he stigmatized as "materialism " or not. 
In such a sense all exact science, and the law of cause and 
effect at its head, is purely materialistic. 

Moral, or ethical Materialism, is something quite distinct 
from scientific materialism, and has nothing whatever in 
common with the latter. This real materialism proposes 
no other aim to man in the course of his life than 
the most refined possible gratification of his senses. It is 
based on the delusion that purely material enjoyment 
can alone give satisfaction to man ; but as he can find that 
satisfaction in no one form of sensuous pleasure, he dashes on 
weariedly from one to another. The profound truth that the 
real value of life does not lie in material enjoyment, but in 
moral action — that true happiness does not depend upon 
external possessions, but only in a virtuous course of life — 
this is unknown to ethical materialism. We therefore look 
in vain for such materialism among naturalists and phi- 
losophers, whose highest happiness is the intellectual 
enjoyment of Nature, and whose highest aim is the know- 
ledge of her laws. We find it in the palaces of ecclesi- 
astical princes, and in those hypocrites who, under the 
outward mask of a pious worship of God, solely aim at 
hierarchical tyranny over, and material spoliation of, their 
fellow-men. Blind to the infinite grandeur of the so-called 


" raw material," and the glorious world of phenomena 
arising from it — insensible to the inexhaustible charms 
of Nature, and without a knowledge of her laws — they 
stigmatize all natural science, and the culture arising from 
it, as sinful " materialism," while really it is this which they 
themselves exhibit in a most shocking form. Satisfactory 
proofs of this are furnished, not only by the whole history 
of the Catholic Popes, with their long series of crimes, but 
also by the history of the morals of orthodoxy in every 
form of religion. 

In order, then, to avoid in future the usual confusion of 
this] utterly objectionable Moral Materialism with our 
Scientific Materialism, we think it necessary to call the 
latter either Monism or Realism. The principle of this 
Monism is the same as what Kant terms the " principle of 
mechanism," and of which he expressly asserts, that without 
it there can be no natural science at all. This principle is 
quite inseparable from our Non-miraculous History of Crea- 
tion, and characterizes it as opposed to the teleological belief 
in the miracles of a Supernatural History of Creation. 

Let us now first of all glance at the most important of all 
the supernatural histories of creation, I mean that of 
Moses, as it has been handed down to us in the Bible, the 
ancient document of the history and laws of the Jewish 
people. The Mosaic history of creation, since in the first 
chapter of Genesis it forms the introduction to the Old 
Testament, has enjoyed, down to the present day, general 
recognition in the whole Jewish and Christian world of 
civilization. Its extraordinary success is explained not 
only by its close connection with Jewish and Christian 
-doctrines, but also by the simple and natural chain of ideas 



which runs through it, and which contrasts favourably 
with the confused mythology of creation current among 
most of the other ancient nations. First the Lord God 
creates the earth as an inorganic body ; then he separates 
light from darkness, then water from the dry land. Now 
the earth has become inhabitable for organisms, and plants 
are first created, animals later — and among the latter the 
inhabitants of the water and the air first, afterwards the 
inhabitants of the dry land. Finally God creates man, the 
last of all organisms, in his own image, and as the ruler of 
the earth. 

Two great and fundamental ideas, common also to the 
non-miraculous theory of development, meet us in this 
Mosaic hypothesis of creation, with surprising clearness and 
simplicity — the idea of separation or differentiation, and the 
idea of progressive development or perfecting. Although 
Moses looks upon the results of the great laws of organic 
development (which we shall later point out as the necessary 
conclusions of the Doctrine of Descent) as the direct actions 
of a constructing Creator, yet in his theory there lies hidden 
the ruling idea of a progressive development and a differen- 
tiation of the originally simple matter. We can therefore 
bestow our just and sincere admiration on the Jewish 
lawgiver's grand insight into nature, and his simple and 
natural hypothesis of creation, without discovering in it a 
so-called " divine revelation." That it cannot be such is clear 
from the fact that two great fundamental errors are asserted 
in it, namely, first, the geocentric error that the earth is the 
fixed central point of the whole universe, round which the 
sun, moon, and stars move; and secondly, the anthropocentric 
error, that man is the premeditated aim of the creation of 


the earth, for whose service alone all the rest of nature is 
said to have been created. The former of these errors was 
demolished by Copernicus' System of the Universe in the 
beginning of the 16th century, the latter by Lamarck's 
Doctrine of Descent in the beginning of the 19th century. 

Although the geocentric error of the Mosaic history was 
demonstrated by Copernicus, and thereby its authority as 
an absolutely perfect divine revelation was destroyed, yet it 
has maintained, down to the present day, such influence, 
that it forms in many wide circles the principle obstacle to 
the adoption of a natural theory of development. Even 
in our century, many naturalists, especially geologists, 
have tried to bring the Mosaic theory into harmony 
with the recent results of natural science, and have, for 
example, interpreted Moses' seven days of creation as seven 
great geological periods. However, all these ingenious 
attempts at interpretation have so utterly failed, that they 
require no refutation here. The Bible is no scientific book, 
but consists of records of the history, the laws, and the 
religion of the Jewish people, the high merit of which, as a 
history of civilization, is not impaired by the fact that in all 
scientific questions it has no commanding importance, and is 
full of gross errors. 

We may now make a great stride over more than three 
thousand years, from Moses, who died about the year 1480 
before Christ, to Linngeus, who was born in the year 1707 
after Christ. During this whole period no history of creation 
was brought forward that gained any lasting importance, or 
the closer examination of which would here be of any 
interest. Indeed, during the last fifteen hundred years, 
since Christianity gained its supremacy, the Mosaic history 


of creation, together with the dogmas connected with it, has 
become so generally predominant, that the 19th century is 
the first that has dared positively to rise against it. Even 
the great Swedish naturalist, Linnaeus, the founder of modern 
natural history, linked his System of Nature most closely to 
the Mosaic history of creation. 

The extraordinary progress which Charles Linnseus made 
in the so-called descriptive natural sciences, consists, as is 
well known, in his having established a system of nomencla- 
ture of animals and plants, which he carried out in a manner 
so perfectly logical and consistent, that down to the present 
day it has remained in many respects the standard for all 
succeeding naturalists engaged in the study of the forms of 
animals and plants. Although Linnseus' system was 
artificial, although in classifying animal and vegetable 
species he only sought and employed single parts as the 
foundation for his divisions, it has, nevertheless, gained the 
greatest success ; firstly, in consequence of its being carried 
out consistently, and secondly, by its nomenclature of natural 
bodies, which has become extremely important, and at 
which we must here briefly glance. 

Before Linnaeus' time, many vain attempts had been made 
to throw light upon the endless chaos of different animal 
and vegetable forms (then known) by adopting for them 
suitable names and groupings ; but Linnseus, by a happy hit, 
succeeded in accomplishing this important and difficult task, 
when he established the so-called " binary nomenclature." 
The binary nomenclature, or the twofold designation, as 
Linnseus first established it, is still universally applied by 
all zoologists and botanists, and will, no doubt, maintain 
itself, for a long time to come, with undiminished authority. 

Linnaeus' nomenclature. 41 

It consists in this, that every species of animal and plant is 
designated by two names, which stand to each other in the 
same relation as do the christian and surnames of a man. 
The special name which corresponds with the christian 
name, and expresses the idea of " a species," serves as the 
common designation of all individual animals or plants, 
which are equal in all essential matters of form, and are 
only distinguished by quite subordinate features. The more 
general name, on the other hand, corresponding with the 
surname, and which expresses the idea of a genus, serves for 
the common designation of all the most nearly similar kinds 
•or species. 

According to Linnseus' plan, the more general and compre- 
hensive generic name is written first ; the special suboi> 
dinate name of the species follows it. Thus, for example, 
the common cat is called Felis domestica; the wild cat, 
Felis catus ; the panther, Felis pardus ; the jaguar, Felis onca ; 
the tiger, Felis tigris ; the lion, Felis leo. All these six kinds 
of animals of prey are different species of one and the 
same genus — Felis. Or, to add an example from the vege- 
table kingdom, according to Linnaeus' designation the pine 
is Pinus abies ; the fir, Pinus picea ; the larch, Pinus larix ; 
the Italian pine, Pinus pinea ; the Siberian stone pine, Pinus 
cembra ; the knee timber, Pinus mughus ; the common pine, 
Pinus silvestris. All these seven kinds of pines are different 
species of one and the same genus — Pinus. 

Perhaps this advance made by Linnseus may seem to some 
only of subordinate importance in the practical distinction 
and designation of the variously formed organisms. But in 
reality it was of the very greatest importance, both from a 
practical and theoretical point of view. For now, for the 


first time, it became possible to arrange the immense mass of 
different organic forms according to their greater or less 
degree of resemblance, and to obtain an easy survey of the 
general outlines of such a " system." Linnaeus facilitated 
the tabulation and survey of this " system " of plants and 
animals still more by placing together the most nearly 
similar genera into so-called orders (ordines) ; and by 
uniting the most nearly similar orders into still more com- 
prehensive main divisions or classes. Thus, according to 
Linnseus, each of the two organic kingdoms were broken up 
into a number of classes, the vegetable kingdom into twenty- 
four, and the animal kingdom into six. Each class again 
contains several orders. Every single order may contain 
a number of genera, and, again, every single genus several 

Valuable as was Linnseus' binary nomenclature in a prac- 
tical way, in bringing about a comprehensive systematic 
distinction, designation, arrangement, and division of the 
organic world of forms, yet the incalculable theoretical 
influence which it gained forthwith in relation to the 
history of creation was no less important. Even now all 
the important fundamental questions as to the history of 
creation turn finally upon the decision of the very 
remote and unimportant question, What really are kinds or 
species ? Even now the idea of organic species may be 
termed the central point of the whole question of creation, 
the disputed centre, about the different conceptions of 
which Darwinists and Anti-Darwinists fight. 

According to Darwin's opinion, and that of his adherents, 
the different species of one and the same genus of animals 
and plants are nothing else than differently developed 


descendants of one and the same original primary form. , 
The different kinds of pine mentioned above would accord- 
ingly have originated from a single primaeval form of pine. 
In like manner the origin of all the species of cat 
mentioned above would be traced to a single common form 
of Felis, the ancestor of the whole genus. But further, 
in accordance with the Doctrine of Descent, all the 
different genera of one and the same order ought also to 
be descended from one common primary ancestor, and so, in 
like manner, all ordres of a class from a single primary form. 
On the other hand, according to the idea of Darwin's 
opponents, all species of animals and plants are quite in- 
dependent of each other, and only the individuals of each 
species have originated from a single primary form. But if 
we ask them how they conceive these original primary forms 
of each species to have come into existence, they answer 
with a leap into the incomprehensible, " They were created." 
Linnaeus himself defined the idea of species in this 
manner by saying, " There are as many different species as 
there were different forms created in the beginning by the 
infinite Being." ( " Species tot sunt diversae, quot diversas 
formas ab initio creavit infinitum ens.") In this respect, 
therefore, he follows most closely the Mosaic history of 
creation, which in the same way maintains that animals 
and plants were created "each one after its kind." Linnaeus, 
accepting this, held that originally of each species of 
animals and plants either a single individual or a pair had 
been created; in fact a pair, or, as Moses says, "a male 
and a female " of those species which have separate sexes, 
but of those species in which each individual combines both 
sexual organs (hermaphrodites), as for instance the earth- 


worm, the garden and vineyard snails, as well as the great 
majority of plants, a single individual. 

Linnaeus further follows the Mosaic legend in regard to the 
flood, by supposing that the great general flood destroyed all 
existing organisms, except those few individuals of each 
species (seven pairs of the birds and of clean animals, one 
pair of unclean animals) which Noah saved in the ark, and 
which were placed again on land, on Mount Ararat, after the 
flood had subsided. He tried to explain the geographical 
difficulty of the living together of the most different animals 
and plants, as follows : Mount Ararat, in Armenia, being 
situated in a warm climate, and rising over 16,000 feet in 
height, combines in itself the conditions for a temporary 
common abode of such animals as live in different zones. 
Accordingly, animals accustomed to the polar regions could 
climb up the cold mountain ridges, those accustomed to 
a warm climate could go down to the foot of the mountain, 
and the inhabitants of a temperate zone could remain mid- 
way up the mountain. From this point it was possible for 
them to spread north and south over the earth. 

It is scarcely necessary to remark that this Linnaean 
hypothesis of creation, which evidently was intended to 
harmonize most closely with the prevailing belief in the 
Bible, requires no serious refutation. When we consider 
Linnaeus' clearness and sagacity in other matters, we may 
doubt whether he believed it himself. As to the simulta- 
neous origin of all individuals of each species from one pair 
of ancestors respectively (or in the case of the hermaphro- 
dite species, from one original hermaphrodite), it is clearly 
quite untenable ; for, apart from other reasons, in the first 
days after the creation, the few animals of prey would have 


sufficed to have utterly demolished all the herbivorous animals, 
as the herbivorous animals must have destroyed the few 
individuals of the different species of plants. The existence 
of such an equilibrium in the economy of nature as obtains 
at present cannot possibly be conceived, if only one individual 
of each species, or only one pair, had originally and simul- 
taneously been created. 

Moreover, how little importance Linnaeus himself attached 
to this untenable hypothesis of creation is clear, among 
other things, from the fact that he recognized Hybridism 
(crossing) as a source of the production of new species. 
He assumed that a great number of independent new 
species had originated by the interbreeding of two different 
species. Indeed, such hybrids are not at all rare in nature, 
and it is now proved that a great number of species, for 
example, of the genus Rubus (bramble), mullen (Verbascum), 
willow (Salix), thistle (Cirsium), are hybrids of different 
species of these genera. We also know of hybrids between 
hares and rabbits (two species of the genus Lepus), further 
of hybrids between different species of dog (genus Canis), 
etc., which can be propagated as independent species. 

It is certainly very remarkable that Linnseus asserted 
the physiological (therefore mechanical) origin of new species 
in this process of hybridism. It clearly stands in direct 
opposition to the supernatural origin of the other species by 
creation, which he accepted as put forward in the Mosaic 
account. The one set of species would therefore have 
originated by dualistic (teleological) creation, the other by 
monistic (mechanical) development. 

The great and well merited authority which Linmeus 
gained by his systematic classification and by his other 


services to Biology, was clearly the reason why his views of 
creation also remained, throughout the whole of the last 
century, undisputed and generally recognized. If through- 
out systematic Zoology and Botany the distinctions, 
classification, and designations of species, introduced by 
Linnaeus, and the dogmatic ideas connected therewith had 
not been maintained — more or less unaltered — we should be 
■at a loss to understand how his idea of an independent 
creation of single species could have stood, by itself, down 
to the present day. It is only owing to his great 
authority, and through his attaching himself to the prevail- 
ing Biblical belief, that his hypothesis of creation has 
retained its position so long. 

( 47 ) 




General Theoretical Meaning of the Idea of Species. — Distinction between 
the Theoretical and Practical Definition of the Idea of Species. — Cuvier's 
Definition of Species. — Merits of Cnvier as the Founder of Comparative 
Anatomy. — Distinction of the Pour Principal Forms (types or branches) 
of the Animal Kingdom, by Cuvier and Bar. — Cuvier's Services to 
Palaeontology. — His Hypothesis of the Revolutions of our Globe, and the 
Epochs of Creation separated by them. — Unknown Supernatural Causes 
of the Revolutions, and the subsequent New Creations. — Agassiz's 
Teleological System of Nature. — His Conception of the Plan of Creation, 
and its six Categories (groups in classification). — Agassiz's Views of the 
Creation of Species.— Rude Conception of the Creator as a man-like 
being in Agassiz's Hypothesis of Creation. — Its internal Inconsistency 
and Contradictions with the important Palseontological Laws discovered 
by Agassiz. 

The real matter of dissension in the contest carried on 
by naturalists as to the origin of organisms, their creation 
and development, lies in the conceptions which are enter- 
tained about the nature of species. Naturalists either 
agree with Linnaeus, and look upon the different species 
as distinct forms of creation, independent of one another, 
or they assume with Darwin their blood-relationship. 
If we share Linnpeus' view (which was discussed in our 
last chapter), that the different organic species came into 
existence independently — that they have no blood-relation- 


ship — we are forced to admit that they were created 
independently, and we must either suppose that every 
single organic individual was a special act of creation 
(to which surely no naturalist will agree), or we must 
derive all individuals of every species from a single in- 
dividual, or from a single pair, which did not arise in a 
natural manner, but was called into being by command of 
a Creator. In so doing, however, we turn aside from the 
safe domain of a rational knowledge of nature, and take 
refuge in the mythological belief in miracles. 

If, on the other hand, with Darwin, we refer the simi- 
larity of form of the different species to real blood-relation- 
ship, we must consider all the different species of animals 
and plants as the altered descendants of one or a few most 
simple original forms. Viewed in this way, the Natural 
System of organisms (that is, their tree-like and branching 
arrangement and division into classes, orders, families, 
genera, and species) acquires the significance of a real genea- 
logical tree, whose root is formed by those original archaic 
forms which have long since disappeared. But a truly 
natural and consistent view of organisms can assume no 
supernatural act of creation for even those simplest original 
forms, but only a coming into existence by spontaneous 
generation* (archigony, or generatio spontanea). From 
Darwin's view of the nature of species, we arrive there- 
fore at a natural theory of development ; but from Lin- 
naeus' conception of the idea of species, we must assume a 
supernatural dogma of creation. 

Most naturalists after Linnseus, whose great services in 

* Archebiosis (Bastian), Abiogenesis (Huxley). 


systematic and descriptive natural history won for him 
such high authority, followed in his footsteps, and without 
further inquiry into the origin of organization, they assumed, 
in the sense of Linnaeus, an independent creation of individual 
species, in conformity with the Mosaic account of creation. 
The foundation of their conception was based upon Lin- 
naeus' words: "There are as many different species as there 
were different forms created in the beginning by the Infinite 
Being." We must here remark at once, without going 
further into the definition of species, that all zoologists and 
botanists in their classificatory systems, in the practical dis- 
tinction and designation of species of animals and plants, 
never troubled, or even could trouble, themselves in the 
slightest degree about this assumed creation of the parent 
forms. In reference to this, one of our first zoologists, the 
ingenious Fritz Miiller, makes the following striking obser- 
vation : " Just as in Christian countries there is a catechism 
of morals, which every one knows by heart, but which no 
one considers it his duty to follow, or expects to see followed 
by others, — so zoology also has its dogmas, which are just 
as generally professed as they are denied in practice." 
(Fiir Darwin, p. 71.) 16 

Linnaeus' venerated dogma of species is just such an 
irrational dogma, and for that very reason it is powerful. 
Although most naturalists blindly submitted to it, yet they 
were, of course, never in a position to demonstrate the descent 
of individuals belonging to one species from the common' 
originally created, primitive form. Zoologists and botanists, 
in their systems of nomenclature, confined themselves 
entirely to the similarity of forms, in order to distinguish 
and name the different species. They placed in one species 

VOL. I. E 


all organic individuals which were very similar, or almost 
identical in form, and which could only be distinguished 
from one another by very unimportant differences. On the 
other hand, they considered as different species those 
individuals which presented more essential or more striking 
differences in the formation of their bodies. But of course 
this opened the flood-gates to the most arbitrary proceedings 
in the systematic distinctions of species. For as all the 
individuals of one species are never completely alike in 
all their parts, but as every species varies more or less, no 
one could point out which degree of variation constituted 
a really " good species," or which degree indicated a "mere 

This dogmatic conception of the idea of species, and 
the arbitrary proceedings connected with it, necessarily 
led to the most perplexing contradictions, and to the most 
untenable suppositions. This is clearly demonstrable in 
the case of the celebrated Cuvier (born in 1769), who 
next to Linnaeus has exercised the greatest influence on 
the study of zoology. In his conception and definition of 
the idea of species, he agreed on the whole with Linnaeus, 
and shared also his belief in an independent creation of 
individual species. Cuvier considered their immutability 
of such importance that he was led to the foolish asser- 
tion — " The immutability of species is a necessary con- 
dition of the existence of scientific natural history." As 
Linnaeus' definition of species did not satisfy him, he 
made an attempt to give a more exact and, for syste- 
matic practice, a more useful definition, in the following 
words : c: All those individual animals and plants belong to 
one species which can be proved to be either descended 


from one another, or from common ancestors, or which are 
as similar to these as the latter are among themselves." 

In dealing with this matter, Cuvier reasoned in the 
following manner : — " In those organic individuals, of which 
we know that they are descended from one and the same 
common form of ancestors — in which, therefore, their com- 
mon ancestry is empirically proved — there can be no doubt 
that they belong to one species, whether they differ much or 
little from one another, or whether they are almost alike or 
very unlike. Moreover, all those individuals also belong to 
this species which differ no more from the latter (those 
proved to be derived from a common stock) than these differ 
from one another." In a closer examination of this definition 
of species given by Cuvier, it becomes at once evident that 
it is neither theoretically satisfactory nor practically appli- 
cable. Cuvier, with this definition, began to move in the 
same circle in which almost all subsequent definitions 
of species have moved, through the assumption of their 

Considering the extraordinary authority which George 
Cuvier has gained in the science of organic nature, and in con- 
sequence of the almost unlimited supremacy which his views 
exercised in zoology, during the first half of our century, it 
seems appropriate here to examine his influence a little more 
closely. This is all the more necessary as we have to com- 
bat, in Cuvier, the most formidable opponent to the Theory 
of Descent and the monistic conception of nature. 

One of the many and great merits of Cuvier is that he 
stands forth as the founder of Comparative Anatomy. While 
Linnseus established the distinction of species, genera, orders, 
and classes mostly upon external characters, and upon sepa- 


rate and easily discoverable signs in the number, size, place, 
and form of individual organic parts of the body, Cuvier 
penetrated much more deeply into the essence of organiza- 
tion. He demonstrated great and wide differences in the 
inner structure of animals, as the real foundation of a 
scientific knowledge and classification of them. He dis- 
tinguished natural families in the classes of animals, and 
established his natural system of the animal kingdom on 
their comparative anatomy. 

The progress from Linnaeus' artificial system to Cuvier's 
natural system was exceedingly important. Linmeus had 
arranged all animals in a single series, which he divided 
into six classes, two classes of Invertebrate, and four classes 
of Vertebrate animals. He distinguished these artificially, 
according to the nature of their blood and heart. Cuvier,. 
on the other hand, showed that in the animal kingdom there 
were four great natural divisions to be distinguished, which 
he termed Principal Forms, or General Plans, or Branches 
of the animal kingdom (Embranchments), namely — 1. The 
Vertebrate animals (Vertebrata) ; 2. The Articulate animals 
(Articulata) ; 3. The Molluscous animals (Mollusca) ; and 4. 
The Radiate animals (Radiata). He further demonstrated 
that in each of these four branches a peculiar plan of struc- 
ture or type was discernible, distinguishing each branch 
from the three others. In the Vertebrate animals it is dis- 
tinctly expressed by the form of the skeleton, or bony 
framework, as also by the structure and position of the 
dorsal nerve-chord, apart from many other peculiarities. 
The Articulate animals are characterized by their ventral 
nerve-chord and their dorsal heart. In Molluscs the sack- 
shaped and non-articulate body is the distinguishing feature. 


The Eadiate animals, finally, differ from the three other 
principal forms by their body being the combination of four 
or more main sections united in the form of radii (antimera). 

The distinction of these four principal forms of animals, 
which has become extremely productive in the development 
of zoology, is commonly ascribed entirely to Cuvier. How- 
ever, the same thought was expressed almost simultaneously, 
and independently of Cuvier, by Bar, one of the greatest 
naturalists, and still living, who did the most eminent service 
in the study of animal development. Bar showed that in the 
development of animals, also, four different main forms (or 
types) must be distinguished. 20 These correspond with 
the four plans of structure in animals, which Cuvier distin- 
guished on the ground of comparative anatomy. Thus, for 
example, the individual development of all Vertebrate ani- 
mals agrees, from the commencement, so much in its funda- 
mental features that the germs or embryos of different 
Vertebrate animals (for example, of reptiles, birds, and 
mammals) in their earlier stages cannot be distinguished at 
all. It is only at a late stage of development that there 
gradually appear the more marked differences of form which 
separate those different classes and orders from one another. 
The plan of structure, which shows itself in the individual 
development of Articulate animals (insects, spiders, crabs), 
is from the beginning essentially the same in all Articulate 
animals, but different from that of all Vertebrate animals. 
The same holds good, with certain limitations, in Molluscous 
and Radiated animals. 

Neither Bar, who arrived at the distinction of the four 
animal types or principal forms through the history of the 
individual development (Embryology), nor Cuvier, who 


arrived at the same conclusion by means of comparative 
anatomy, recognized the true cause of this difference. 
This is disclosed to us by the Theory of Descent. The 
wonderful and astonishing similarity in the inner organ- 
ization and in the anatomical relations of structure, and 
the still more remarkable agreement in the embryonic de- 
velopment of all animals belonging to one and the same 
type (for example, to the branch of the Vertebrate animals), 
is explained in the simplest manner by the supposition of 
their common descent from a single primary original form. 
If this view is not accepted, then the complete agreement of 
the most different Vertebrate animals, in their inner struc- 
ture and their manner of development, remains perfectly 
inexplicable. In fact it can only be explained by the law of 

Next to the comparative anatomy of animals and the 
systematic zoology founded anew by it, it was specially to 
the science of petrifactions, or Palaeontology, that Cuvier 
rendered great service. We must draw special attention 
to this, because these very palseontological views, and the 
geological ideas connected with them, were held almost 
universally in the highest esteem during the first half of 
the present century, and caused the greatest hindrance to 
the working out of a truly natural history of creation. 

Petrifactions, the scientific study of which Cuvier pro- 
moted at the beginning of our century in a most ex- 
tensive manner, and established quite anew for the Verte- 
brate animals, play one of the most important parts in the 
" non-miraculous history of creation." For these remains 
and impressions of extinct animals and plants, preserved to 
us in a petrified condition, are the true " monuments of the 


creation/' the infallible and indisputable records which fix 
the correct history of organisms upon an irrefragable founda- 
tion. All petrified or fossil remains and impressions tell us 
of the forms and structure of such animals and plants as are 
either the progenitors and ancestors of the present living 
organisms, or they are the representatives of extinct colla- 
teral lines, which, together with the present living organisms, 
branched off from a common stem. 

These inestimable records of the history of creation 
throughout a long period played a subordinate part in 
science. Their true nature was indeed correctly understood, 
even more than five hundred years before Christ, by the 
great Greek philosopher, Xenophanes of Colophon, the same 
who founded the so-called Eleatic philosophy, and who was 
the first to demonstrate with convincing precision that all 
conceptions of personal gods result in more or less rude 

Xenophanes for the first time asserted that the fossil im- 
pressions of animals and plants were real remains of formerly 
living creatures, and that the mountains in whose rocks 
they were found must at an earlier date have stood under 
water. But although other great philosophers of antiquity, 
and among them Aristotle, also possessed this true know- 
ledge, yet throughout the illiterate Middle Ages, and even 
with some naturalists of the last century, the idea prevailed 
that petrifactions were so-called freaks of nature (lusus 
naturae), or products of an unknown formative power or 
instinct of nature (nisus formativus, vis plastica). Kespect- 
ing the nature of this mysterious and mystic creative 
power, the strangest ideas were formed. Some believed that 
this constructive power — the same to which they also 


ascribed the coming into existence of the present species of 
animals and plants — had made numerous attempts to create 
organisms of different forms, but that these attempts had 
only partially succeeded, had often failed, and that petrifac- 
tions were nothing more than such unsuccessful attempts. 
According to others, petrifactions originated from the in- 
fluence of the stars upon the interior of the earth. 

Others, again, had the still cruder notion that the Creator 
had first made models (out of mineral substances — for 
example, of gypsum or clay) of those forms of animals and 
plants which he afterwards executed in organic substances, 
and into which he breathed his living breath ; petrifactions 
were accordingly such rude inorganic models. Even as late 
as the last century these crude ideas prevailed, and it was 
assumed, for example, that there existed a special " seminal 
air," which was said to penetrate into the earth with 
the water, and by fructifying the stones formed petrifactions 
or " stony flesh " (caro fossilis). 

It took a very long time before the simple and natural 
view was accepted, namely, that petrifactions are in reality 
nothing but what they appear to simple observation — the 
indestructible remains of extinct organisms. It is true the 
celebrated painter, Leonardo da Vinci, in the 15 th century, 
ventured to assert that the mud which was constantly 
deposited by water was the cause of petrifactions, as it 
surrounded the indestructible shells of mussels and snails 
which lay at the bottom of the waters, and gradually turned 
them into solid stone. The same idea, was maintained in 
the 16th century by a Parisian potter, Palissy by name, 
who became celebrated on account of his invention of 
china. However, the so-called "professional men" were 


very far from paying any regard to these correct assertions 
of a simple and healthy human understanding; it was 
not till the end of the last century that it was generally 
accepted, in consequence of the foundation of the Neptunian 
geology by Werner. 

The foundation of a more strictly scientific palaeontology, 
however, belongs to the beginning of our century, when 
Cuvier published his classic researches on petrified Verte- 
brate animals, and when his great opponent, Lamarck, made 
known his remarkable investigations on fossil Invertebrate 
animals, especially on petrified snails and clams. In Cuvier's 
celebrated work "On the Fossil Bones" of Vertebrate animals 
— principally of mammals and reptiles — we see that he had 
already arrived at the knowledge of some very important 
and general palseontological laws, which are of great con- 
sequence to the history of creation. Foremost among them 
stands the assertion that the extinct species of animals, 
whose remains we find petrified in the different strata of 
the earth's crust, lying one above another, differ all the 
more strikingly from the still living kindred species 
of animals the deeper those strata lie — in other words, the 
earlier the animals lived in past ages. In fact, in every per- 
pendicular section of the stratified crust of the earth we 
find that the different strata, deposited by the water in a 
certain historical succession, are characterized by different 
petrifactions, and that these extinct organisms become more 
like those of the present day the higher the strata lie ; in 
other words, the more recent the period in the earth's 
history in which they lived, died, and became encrusted by 
the deposited and hardened strata of mud. 

However important this general observation of Cuvier's 


was in one sense, yet in another it became to him the source 
of a very serious error. For as he considered the charac- 
teristic petrifactions of each individual group of strata 
(which had been deposited during one main period of the 
earth's history) to be entirely different from those of the 
strata lying above or below, and as he erroneously believed 
that one and the same species of animal was never found in 
two succeeding groups of strata, he arrived at the false idea, 
which was accepted as a law by most subsequent naturalists, 
that a series of quite distinct periods of creation had 
succeeded one another. Each period was supposed to have 
had its special animal and vegetable world, each its peculiar 
specific Fauna and Flora. 

Cuvier imagined that the whole history of the earth's 
crust, since the time when living creatures had first appeared 
on the surface, must be divided into a number of perfectly 
distinct periods, or divisions of time, and that the individual 
periods must have been separated from one another by 
peculiar revolutions of an unknown nature (cataclysms, or 
catastrophes). Each revolution was followed by the utter 
annihilation of the till then existing animals and plants, and 
after its termination a completely new creation of organic 
forms took place. A new world of animals and plants, 
absolutely and specifically distinct from those of the preced- 
ing historical periods, was called into existence at once, and 
now again peopled the globe for thousands of years, till it 
again perished suddenly in the crash of a new revolution. 

About the nature and causes of these revolutions, Cuvier 
expressly said that no idea could be formed, and that the 
present active forces in nature were not sufficient for their 
explanation. Cuvier points out four active causes as the 

cuvier's cataclysms. 59 

natural forces, or mechanical agents, at present constantly 
but slowly at work in changing the earth's surface : first, 
rain, which washes down the steep mountain slopes 
and heapes up debris at their foot; secondly, flowing 
waters, which carry away this de'bris and deposit 
it as mud in stagnant waters; thirdly, the sea, whose 
breakers gnaw at the. steep sea coasts, and throw up 
"dunes" on the flat sea margins; finally and fourthly, 
vblcanos, which break through and heave up the strata of 
the earth's hardened crust, and pile up and scatter about the 
products of their eruptions. Whilst Cuvier recognizes the 
constant slow transformation of the present surface of the 
earth by these four mighty causes, he asserts at the same 
time that they would not have sufficed to effect the 
revolutions of the remote ages, and that the anatomical 
structure of the earth's surface cannot be explained by 
the necessary action of those mechanical agents : the great 
and marvellous revolutions of the whole earth's surface 
must, according to him, have been rather the effects of very 
peculiar causes, completely unknown to us ; the usual thread 
of development was broken by them, and the course of 
nature altered. 

These views Cuvier explained in a special work " On the 
Revolutions of the Earth's Surface, and the Changes which 
they have wrought in the Animal World." They were 
maintained, and generally accepted for a long time, and be- 
came the greatest obstacle to the development of a natural 
history of the creation. For if such all-destructive revolu- 
tions had actually occurred, of course a continuity of the 
development of species, a connecting thread in the organic 
history of the earth, could not be admitted at all, and we 


should be obliged to have recourse to the action of super- 
natural forces ; that is, to the interference of miracles in the 
natural course of things. It is only through miracles that 
these revolutions of the earth could have been brought about, 
and it is only through miracles that, after their cessation 
and at the commencement of each new period, a new animal 
and vegetable kingdom could have been created. But 
science has no room for miracles, for by miracles we under- 
stand an interference of supernatural forces in the natural 
course of development of matter. 

Just as the great authority which Linnaeus gained by 
his system of distinguishing and naming organic species 
led his successors to a complete ossification, as it were, of the 
dogmatic idea of species and to a real abuse of the syste- 
matic distinction implied by it, so the great services which 
Cuvier had rendered to the knowledge and distinction 
of extinct species became the cause of a general adoption 
of his theory of revolutions and catastrophes, and of the 
false views of creation connected therewith. The conse- 
quence of this was that, during the first half of our century, 
most zoologists and botanists clung to the opinion that a 
series of independent periods in the organic history of the 
earth had existed; that each period was distinguished by 
distinct and peculiar kinds of animal and vegetable species ; 
that these were annihilated at the termination of the period 
by a general revolution ; and that, after the cessation of the 
latter, a new world of different species of animals and plants 
was created. 

It is true some independent thinkers, above all the great 
physical philosopher, Lamarck, even at an early period, set 
forth a series of weighty reasons which refuted Cuvier's 


theory of cataclysms, and pointed to a perfectly continuous 
and uninterrupted developmental history of all the organic 
inhabitants of the earth through all ages. They maintained 
that the animal and vegetable species of each period were 
derived from those of the preceding period, and were only 
the altered descendants of the former. This true conception, 
however, being opposed to Cuvier's great authority, was 
then unable to make way. Nay, even after Cuvier's theory 
of catastrophies had been completely cast out from the 
domain of geology by Lyell's classic Principles of Geology, 
which appeared in 1830, still his idea of the specific dis- 
tinctness of a series of organic creations maintained its- 
influence, in many ways, in the science of Palaeontology. 
(Gen. Morph. ii. 312.) 

By a curious coincidence, thirteen years ago, almost at 
the same time that Cuvier's History of Creation received its 
death-blow by Darwin's book, another celebrated naturalist 
made an attempt to re-establish it, and to adopt it in the 
roughest manner, as a part of a teleologico-theological 
system of nature. This was the Swiss geologist, Louis. 
Agassiz, who attained a great reputation by his theory 
of glaciers and the ice-period, borrowed from Schimper and 
Charpentier, and who has been riving in North America for 
many years. He commenced in 1858 to publish a work 
planned on a very large scale, which bears the title of 
" Contributions to the Natural History of the United States- 
of North America." The first volume of this work, although 
large and costly, owing to the patriotism of the Americans, 
had an unprecedented sale ; its title is, " An Essay on Classi- 
fication." 5 

In this essay Agassiz not only discusses the natural series 


of organisms, and the different attempts of naturalists at 
classification, but also all the general biological phenomena 
which have reference to it. The history of the development 
of organisms, both the embryonal and the palaeontologieal, 
comparative anatomy, the general economy of nature, the 
geographical and topographical distribution of animals and 
plants — in short, almost all the general phenomena of 
organic nature are discussed in Agassiz's Essay on Classifi- 
cation, and are explained in a sense and from a point of 
view which is thoroughly opposed to that of Darwin. 
While Darwin's chief merit lies in the fact that he demon- 
strates natural causes for the coming into existence of 
animal and vegetable species, and thereby establishes the 
mechanical or monistic view of the universe as regards this 
most difficult branch of the history of creation, Agassiz, on 
the contrary, strives to exclude every mechanical hypothesis 
from the subject, and to put the supernatural interference 
of a personal Creator in the place of the natural forces 
of matter ; consequently, to establish a thoroughly teleo- 
logical or dualistic view of the universe. It will not be 
out of place if I examine a little more closely Agassiz's 
biological views, and especially his ideas of creation, 
because no other work of our opponents treats the important 
fundamental questions with equal minuteness, and because 
the utter untenableness of the dualistic conception of nature 
becomes very evident from the failure of this attempt. 

The organic species, the various conceptions of which we 
have above designated as the real centre of dispute in the 
opposed views of creation, is looked upon by Agassiz, as 
by Cuvier and Linnaeus, as a form unchangeable in all its 
essential characteristics. The species may indeed change 


and vary within certain narrow limits ; never in essential 
qualities, but only in unessential points. No new species 
could ever proceed from the changes or varieties of a species. 
Not one of all organic species, therefore, is ever derived from 
another, but each individual species has been separately 
created by God. Each individual species, as Agassiz 
expresses it, is "an embodied creative thought " of God. 

In direct opposition to the fact established by palseonto- 
logical experience, that the duration of the individual 
organic species is most unequal, and that many species 
continue unchanged through several successive periods of 
the earth's history, while others only existed during a small 
portion of such a period, Agassiz maintains that one and 
the same species never occurs in two different periods, but 
that each individual period is characterized by species of 
animals and plants which are quite peculiar, and belong to 
it exclusively. He further shares Cuvier's opinion that the 
whole of these inhabitants were annihilated by the great 
and universal revolutions of the earth's surface, which 
divide two successive periods, and that after its destruction 
a new and specifically different assemblage of organisms was 
created. This new creation Agassiz supposes to have taken 
place in this manner : viz., that at each creation all the 
inhabitants of the earth, in their full average number of 
individuals, and in the peculiar relations corresponding 
to the economy of nature, were, as a whole, suddenly placed 
upon the earth by the Creator. In saying this he puts 
himself in opposition to one of the most firmly established 
and most important laws of animal and vegetable geography 
— namely, to the law that each species has a single original 
locality of origin, or a so-called " centre of creation," from 


which it has gradually spread over the rest of the earth. 
Instead of this, Agassiz assumes each species to have been 
created at several points of the earth's surface, and that in 
each case a large number of individuals was created. 

The " natural system " of organisms, the different groups 
and categories of which arranged above one another — » 
namely, the branches, classes, orders, families, genera, and 
species — we consider, in accordance with the Theory of 
Descent, as different branches and twigs of the organic family- 
tree, is, according to Agassiz, the direct expression of the 
divine plan of creation, and the naturalist, while investigat- 
ing the natural system, repeats the creative thoughts of God. 
In this Agassiz finds the strongest proof that man is the 
image and child of God. The different stages of groups or 
categories of the natural system correspond with the different 
stages of development which the divine plan of creation 
had attained. The Creator, in projecting and carrying out 
this plan, starting from the most general ideas of creation, 
plunged more and more into specialities. For instance, 
when creating the animal kingdom, God had in the first 
place four totally distinct ideas of animal bodies, which he 
embodied in the different structures of the four great, 
principal forms, types, or branches of the animal kingdom; 
namely, vertebrate animals, articulate animals, molluscous 
animals, and radiate animals. The Creator then, having 
reflected in what manner he might vary these four different 
plans of structure, next created within each of the four 
principal forms, several different classes — for example, in 
the vertebrate animal form, the classes of mammals, 
birds, reptiles, amphibious animals, and fishes. Then 
God further reflected upon the individual classes, and by 


various modifications in the structure of each class, he pro- 
duced the individual orders. By further variation in the 
order, he created natural families. As the Creator further 
varied the peculiarities of structure of individual parts in 
each family, genera arose. In further meditation on his 
plan of creation, he entered so much into detail that in- 
dividual species came into existence, which, consequently, 
ai*e embodied creative thoughts of the most special kind. 
It is only to be regretted that the Creator expressed these 
most special and most deeply considered "creative thoughts" 
in so very indistinct and loose a manner, and that he im- 
printed so vague a stamp upon them, and permitted them to 
vary so freely that not one naturalist is able to distinguish 
the "good" from the "bad species," or a genuine species 
from varieties, races, etc. (Gen. Morph. ii. 373.) 

We see, then, according to Agassiz's conception, that the 
Creator, in producing organic forms, goes to work exactly 
as a human architect, who has taken upon himself the task 
of devising and producing as many different buildings as 
possible, for the most manifold purposes, in the most dif- 
ferent styles, in various degrees of simplicity, splendour, 
greatness, and perfection. This architect would perhaps at 
first choose four different styles for all these buildings, say 
the Gothic, Byzantine, Chinese, and Rococo styles. In each 
of these styles he would build a number of churches, palaces, 
garrisons, prisons, and dwelling-houses. Each of these dif- 
ferent buildings he would execute in ruder and more perfect, 
in greater and smaller, in simpler and grander fashion, etc. 
However, the human architect would perhaps, in this 
respect, be better off than the divine Creator, as he would 
have perfect liberty in the number of graduated subordinate 

VOL. I. F 


groups. The Creator, however, according to Agassiz, can 
only move "within six groups or categories : the species, 
genus, family, order, class, and type. More than these six 
categories do not exist for him. 

When we read Agassiz's hook on classification, and see 
how he carries out and establishes these strange ideas, we can 
scarcely understand how, with all the appearance of scien- 
tific earnestness, he can persevere in his idea of the divine 
Creator as a man-like being (anthropomorphism), for by his 
explanation of details he produces a picture of the most 
absurd nonsense. In the whole series of these suppositions 
the Creator is nothing but an all-mighty man, who, plagued 
with ennui, amuses himself with planning and constructing 
most varied toys in the shape of organic species. After 
having diverted himself with these for thousands of years, 
they become tiresome to him, he destroys them by a general 
revolution of the earth's surface, and thus throws the whole 
of the useless toys in heaps together ; then, in order to 
while away his time with something new and better, he 
calls a new and more perfect animal and vegetable world 
into existence. But in order not to have the trouble of 
beginning the work of creation over again, he keeps, in the 
main, to his original plan of creation, and creates merely 
new species, or at most only new genera, and much more 
rarely new families, new orders, or classes. He never suc- 
ceeds in producing a new style or type, and always keeps 
strictly within the six categories or graduated groups. 

When, according to Agassiz, the Creator has thus amused 
himself for thousands of millions of years with constructing 
and destroying a series of different creations, at last (but 
very late) he is struck with the happy thought of creating 


something like himself, and so makes man in his own image. 
The end of all the history of creation is thus arrived at 
and the series of revolutions of the earth is closed. Man, 
the child and image of God, gives him so much to do, causes 
him so much pleasure and trouble, that he is wearied no 
longer, and therefore need not undertake a new creation. 
It is clear that if, according to Agassiz, we once assign 
to the Creator entirely human attributes and qualities, and 
regard his work of creation as entirely analogous to human 
creative activity, we are necessarily obliged to admit such 
utterly absurd inferences as those just stated. 

The many intrinsic contradictions and perversities in 
Agassiz's view of creation — a view which necessarily led 
him to the most decided opposition to the Theory of 
Descent — must excite our astonishment all the more be- 
cause, in his earlier scientific works, he had in many 
respects actually paved the way for Darwin, especially 
by his researches in Palaeontology. Among the numerous 
investigations which created general interest in the then 
young science of Palaeontology, those of Agassiz, especially 
his celebrated work on " Fossil Fish," rank next in import- 
ance to Cuvier's work, which formed the foundation of the 
science. The petrified fish, with which Agassiz has made 
us acquainted, have not only an extremely great import- 
ance for the understanding of all groups of Vertebrate 
animals, and their historical development, but we have 
arrived through them at a sure knowledge of important 
general laws of development, some of which were first 
discovered by Agassiz. He it was who drew special atten- 
tion to the remarkable parallelism between the embryonal 
and the palseontological development — between ontogeny 


and phylogeny, which I have already (p. 10) claimed as 
one of the strongest pillars of the Theory of Descent. No 
one before had so distinctly stated as Agassiz did, that, of 
the Vertebrate animals, fishes alone existed, at first, that 
amphibious animals came later, and that birds and mam- 
mals appeared only at a much later period ; further, that 
among mammals, as among fishes, imperfect and lower 
orders had appeared first, but more perfect and higher- 
orders at a later period. Agassiz, therefore, showed that 
the palseontological development of the whole Vertebrate 
group was not only parallel with the embryonic, but also 
with the systematic development, that is, with the graduated 
series which we see everywhere in the system, ascending 
from the lower to the higher classes, orders, etc. 

In the earth's history lower forms appeared first, the 
higher forms later. This important fact, as well as the 
agreement of the embryonic and palseontological develop- 
ment, is explained quite simply and naturally by the 
Doctrine of Descent, and without it is perfectly inex- 
plicable. This cause holds good also in the great law of 
progressive development, that is, of the historical progress 
of oi-ganization, which is traceable, broadly and as a whole, 
in the historical succession of all organisms, as well as in 
the special perfecting of individual parts of animal bodies^ 
Thus, for example, the skeleton of Vertebrate animals 
acquired at first slowly, and by degrees, that high degree 
of perfection which it now possesses in man and the other 
higher Vertebrate animals. Thi3 progress, acknowledged 
in point of fact by Agassiz, necessarily follows from Dar- 
win's Doctrine of Descent, which demonstrates its active 
causes. If this doctrine is correct, the perfecting and diver- 


sification of animal and vegetable species must of necessity 
have gradually increased in the coiuse of the organic history 
of the earth, and could only attain its highest perfection in 
most recent times. 

The above-mentioned laws of development, together with 
some other general ones, which have been expressly admitted 
and justly emphasized by Agassiz, and some of which have 
first been set forth by him, are, as we shall see later, only 
explicable by the Theory of Descent, and without it remain 
perfectly incomprehensible. The conjoint action of In- 
heritance and Adaptation, as explained by Darwin, can 
alone be their true cause. But they all stand in sharp and 
irreconcilable opposition to the hypothesis of creation main- 
tained by Agassiz, as well as to the idea of a personal 
Creator who acts for a definite purpose. If we seriously 
wish to explain those remarkable phenomena and their 
inter-connection by Agassiz's theory, then we are necessarily 
•driven to the curious supposition that the Creator himself 
has developed, together with the organic nature which he 
•created and modelled. We can, in that case, no longer rid 
•ourselves of the idea that the Creator himself, like a human 
being, designed, improved, and finally, with many altera- 
tions, carried out his plans. " Man grows as higher grow 
his aims," and the same supposition, so unworthy of a God, 
must be applied to him. Although, from the reverence 
with which, in every page, Agassiz speaks of the Creator, 
it might appear that, on his theory, we attain to the 
sublimest conception of the divine activity in nature, yet 
the contrary is in truth the case. The divine Creator is 
degraded to the level of an idealized man, of an organism 
progressing in development ! 


Considering the wide popularity and great authority 
which Agassiz's work has gained, and which is perhaps 
justified on account of earlier scientific services rendered by 
the author, I have thought it my duty here to show the 
utter untenableness of his general conceptions. So far as 
this work pretends to be a scientific history of creation, it 
is undoubtedly a complete failure. But still it has great 
value, being the only detailed attempt, adorned with scien- 
tific arguments, which an eminent naturalist of our day 
has made to found a teleological or dualistic history of 
creation. The utter impossibility of such a history has 
thus been made obvious to every one. No opponent of 
Agassiz could have refuted the dualistic conception of 
organic nature and its origin more strikingly than he him- 
self has done by the intrinsic contradictions which present 
themselves everywhere in his theory. 

The opponents of the monistic or mechanical conception 
ot the world have welcomed Agassiz's work with delight, 
and find in it a perfect proof of the direct creative action of 
a personal God. But they overlook the fact that this per- 
sonal Creator is only an idealized organism, endowed with 
human attributes. This low dualistic conception of God 
corresponds with a low animal stage of development of 
the human organism. The more developed man of the pre- 
sent day is capable of, and justified in, conceiving that 
infinitely nobler and sublimer idea of God which alone is 
compatible with the monistic conception of the universe, and 
which recognizes God's spirit and power in all phenomena 
without exception. This monistic idea of God, which belongs 
to the future, has already been expressed by Giordano 
Bruno in the following words: — "A spirit exists in alL 


things, and no body is so small but contains a part of the 
divine substance within itself, by which it is animated." It 
is of this noble idea of God that Goethe says : — "Certainly 
there does not exist a more beautiful worship of God than 
that which needs no image, but which arises in our heart 
from converse with Nature." By it we arrive at the sublime 
idea of the Unity of God and Nature. 





Scientific Insufficiency of all Conceptions of a Creation of Individual Species. 
— Necessity of the Counter Theories of Development. — Historical 
Survey of the Most Important Theories of Development. — Aristotle. — 
His Doctrine of Spontaneous Generation. — The Meaning of Natural 
Philosophy. — Goethe. — His Merits as a Naturalist. — His Metamorphosis 
of Plants. — His Vertebral Theory of the Skull. — His Discovery of the 
Mid Jawbone in Man. — Goethe's Interest in the Dispute between 
Cuvier and Geoffroy St. Hilaire. — Goethe's Discovery of the Two Organic 
Formative Principles, of the Conservative Principle of Specification (by 
inheritance), and of the Progressive Principle of Transformation (by 
Adaptation). —Goethe's Views of the Common Descent of all Vertebrate 
Animals, including Man. — Theory of Development according to Gottfried 
Reinhold Treviranus. — His Monistic Conception of Nature. — Oken. — His 
Natural Philosophy. — Oken's Theory of Protoplasm. — Oken's Theory 
of Infusoria (Cell Theory). — Oken's Theory of Development. 

All the different ideas which we may form of a separate 
and independent origin of the individual organic species 
by creation lead us, when logically carried out, to a so- 
called anthropomorphism, that is, to imagining the Creator 
as a man-like being, as was shown in our last chapter. 
The Creator becomes an organism who designs a plan, 
reflects upon and varies this plan, and finally forms 
creatures according to this plan, as a human architect 
would his building. If even such eminent naturalists as 


Linnasus, Cuvier, and Agassiz, the principal representatives 
of the dualistic hypothesis of creation, could not arrive at a 
more satisfactory view, we may take it as evidence of the 
insufficiency of all those conceptions which would derive 
the various forms of organic nature from a creation of 
individual species. 

Some naturalists, indeed, seeing the complete insuffi- 
ciency of these views, have tried to replace the idea of a 
personal Creator by that of an unconsciously active and 
■creative Force of Nature ; yet this expression is evidently 
merely an evasive phrase, as long as it is not clearly shown 
what this force of nature is, and how it works. Hence 
these attempts, also, have been absolute failures. In fact, 
whenever an independent origin of the different forms of 
animals and plants has been assumed, naturalists have 
found themselves compelled to fall back upon so many "acts 
of creation," that is, on supernatural interferences of the 
Creator in the natural course of things, which in all other 
•cases goes on without interference. 

It is true that several teleological naturalists, feeling 
the scientific insufficiency of a supernatural " creation" 
have endeavoured to save the hypothesis by wishing it to 
be understood that creation " is nothing else than a way of 
coming into being, unknown and inconceivable to us." The 
eminent Fritz Muller has cut off from this sophistic evasion 
every chance of escape by the following striking remark : — 
" It is intended here only to express in a disguised manner 
the shamefaced confession, that they neither have, nor care 
to have, any opinion about the origin of species. Accord- 
ing to this explanation of the word, we might as well speak 
of the creation of cholera, or syphilis, of the creation of a 


conflagration, or of a railway accident, as of the creation of 
man." (Jenaische Zestscrift, bd. v. p. 272.) 

In the face, then, of these hypotheses of creation, which 
are scientifically insufficient, we are forced to seek refuge in 
the counter-theory of development of organisms, if we wish 
to come to a rational conception of the origin of organ- 
isms. We are forced and obliged to do so, even if the theory 
of development only throws a glimmer of probability 
upon a mechanical, natural origin of the animal and vege- 
table species; but all the more if, as we shall see, this 
theory explains all facts simply and clearly, as well as com- 
pletely and comprehensively. The theories of develop- 
ment are by no means, as they often falsely are represented 
to be, arbitrary fancies, or wilful products of the imagination, 
which only attempt approximately to explain the origin of 
this or that individual organism; but they are theories 
founded strictly on science, which explain in the simplest 
manner, from a fixed and clear point of view, the whole of 
organic natural phenomena, and more especially the origin 
of organic species, and demonstrate them to be the necessary 
consequences of mechanical processes in nature. 

As I have already shown in the second chapter, all 
these theories of development coincide naturally with that 
general theory of the universe which is usually designated 
as the uniform or monistic, often also as the mechanical or 
causal, because it only assumes mechanical causes, or causes 
working by necessity (causae efficientes), for the explanation 
of natural phenomena. In like manner, on the other hand, 
the supernatural hypotheses of creation which we have al- 
ready discussed coincide completely with the opposite view 
of the universe, which in contrast to the former is called the 


twofold or dualistic, often the ideological or vital, because 
it traces the organic natural phenomena to final causes, 
acting and working for a definite purpose (causpe finales). 
It is this deep and intrinsic connection of the different 
theories of creation with the most important questions of 
philosophy that incites us to their closer examination. 

The fundamental idea, which must necessarily he at the 
bottom of all natural theories of development, is that of a 
gradual development of all (even the most perfect) or- 
ganisms out of a single, or out of a very few, quite simple, 
and quite imperfect original beings, which came into exist- 
ence, not by supernatural creation, but by spontaneous- 
generation, or archigony, out of inorganic matter. In 
reality, there are two distinct conceptions united in this- 
fundamental idea, but which have, nevertheless, a deep in- 
trinsic connection — namely, first, the idea of spontaneous 
generation (or archigony) of the original primary beings ; 
and secondly, the idea of the progressive development of 
the various species of organisms from those most simple 
primary beings. These two important mechanical concep- 
tions are the inseparable fundamental ideas of every theory 
of development, if scientifically carried out. As it maintains 
the derivation of the different species of animals and plants 
from the simplest, common primary species, we may term 
it also the Doctrine of Filiation, or Theory of Descent; as 
there is also a change of species connected with it, it may 
also be termed the Transmutation Theory. 

While the supernatural histories of creation must have 
originated thousands of years ago, in that very remote 
primitive age when man, first developing out of the monkey- 
state, began for the first time to think more closely about 


himself, and about the origin of the world around him, the 
natural theories of development, on the other hand, are 
necessarily of much more recent origin. These views are 
met with only among nations of a more matured civilization, 
to whom, by philosophic culture, the necessity of a know- 
ledge of natural causes has become apparent; and even among 
these, only individual and specially gifted natures can be 
expected to have recognized the origin of the world of 
phenomena, as well as its coruse of development, as the 
necessary consequences of mechanical, naturally active 
causes. In no nation have these preliminary conditions, for 
the origin of a natural theory of development, ever existed 
in so high a degree as among the Greeks of classic antiquity. 
But, on the other hand, they lacked a close acquaintance 
with the facts of the processes and forms of nature, and, 
consequently, the foundation based upon experience, for a 
satisfactory unravelling of the problem of development. 
Exact investigation of nature, and the knowledge of nature 
founded on an experimental basis, was of course almost 
unknown to antiquity, as well as to the Middle Ages, and 
is only an acquisition of modern times. We have therefore 
here no special occasion to examine the natural theories 
of development of the various Greek philosophers, since 
they were wanting in the knowledge gained by experience, 
both of organic and inorganic nature, and since they 
almost always, as the consequence, lost themselves in airy 

One man only must be mentioned here by way of 
exception, — Aristotle, the greatest and the only truly great 
naturalist of antiquity and the Middle Ages, one of the 
grandest geniuses of all time. To what a degree he stands 


there alone, during a period of more than two thousand 
years, in the region of empirico-philosophical knowledge of 
nature, and especially in his knowledge of organic nature, is 
proved to us by the precious remains of his but partially 
surviving works. In them many traces are found of a 
theory of natural development. Aristotle assumes, as a 
matter of certainty, that spontaneous generation was the 
natural manner in which the lower organic creatures came 
into existence. He describes animals and plants originating 
from matter itself, through its own original force ; as, for 
example, moths from wool, fleas from putrid dung, wood-lice 
from damp wood, etc. But as the distinction of organic 
species, which Linnaeus only arrived at two thousand years 
later, was unknown to him, he could form no ideas about 
their genealogical relations. 

The fundamental notion of the theory of development, 
that the different species of animals and plants have been 
developed from a common primary species by transformation, 
could of course only be clearly asserted after the kinds or 
species themselves had become better known, and after the 
extinct species had been carefully examined and compared 
with the living ones. This was not done until the end 
of the last and the beginning of the present century. 
It was not until the year 1801 that the great Lamarck 
expressed the theory of development, which he, in 1809, 
further elaborated in his classical " Philosophie Zoologique." 
While Lamarck and his countryman, Geoffroy St. Hilaire, in 
France, opposed Cuvier's views, and maintained a natural 
development of organic species by transformation and 
descent, Goethe and Oken at the same time pursued the 
same course in Germany, and helped to establish the theory 


of development. As these naturalists are generally called 
nature-philosophers (Naturphilosophen), and as this 
ambiguous designation is correct in a certain sense, it 
appears to me appropriate here to say a few words about 
the correct estimate of the " jSTaturphilosophie." 

Although for many years in England the ideas of natural 
science and philosophy have been looked upon as almost 
■equivalent, and as every truly scientific investigator of 
nature is most justly called there a " natural philosopher," 
yet in Germany for more than half a century natural science 
has been kept strictly distinct from philosophy, and the union 
of the two into a true philosophy of nature is recognized 
only by the few. This misapprehension is owing to the 
fantastic eccentricities of earlier German natural-philosophers, 
such as Oken, Schelling, etc. ; they believed that they were 
able to construct the laws of nature in their own heads, 
without being obliged to take their stand upon the grounds 
of actual experience. When the complete hollowness of 
their assumptions had been demonstrated, naturalists, in 
'"the nation of thinkers," fell into the very opposite extreme, 
believing that they would be able to reach the high aim of 
science, that is, the knowledge of troth, by the mere experi- 
ence of the senses, and without any philosophical activity of 

From that time, but especially since 1830, most naturalists 
have shown a strong aversion to any general, philosophical 
view of nature. The real aim of natural science was now 
supposed to consist in the knowledge of details, and it was 
believed that this would be attained in the study of biology, 
when the forms and the phenomena of life, in all individual 
organisms, had become accurately known, by the help of the 


finest instruments and means of observation. It is true that 
among these strictly empirical, or so-called exact naturalists, 
there were always very many who rose above this narrow 
point of view, and sought the final aim in a knowledge of 
the general laws of organization. Yet the great majority of 
zoologists and botanists, during the thirty or forty years 
preceding Darwin, refused to concern themselves about such 
general laws; all they admitted was, that perhaps in the far 
■distant future, when the end of all empiric knowledge should 
have been arrived at, when all individual animals and plants 
should have been thoroughly examined, naturalists might 
begin to think of discovering general biological laws. 

If we consider and compare the most important advances 
which the human mind has made in the knowledge of 
truth, we shall soon see that it is always owing to philo- 
sophical mental operations that these advances have been 
made, and that the experience of the senses which certainly 
and necessarily precedes these operations, and the knowledge 
of details gained thereby, only furnish the basis for those 
general laws. Experience and philosophy, therefore, by no 
means stand in such exclusive opposition to each other as 
most men have hitherto supposed ; they rather necessarily 
•supplement each other. The philosopher who is wanting in 
the firm foundation of sensuous experience, of empirical 
knowledge, is very apt to arrive at false conclusions in his 
general speculations, which even a moderately informed 
naturalist can refute at once. On the other hand, the purely 
empiric naturalists, who do not trouble themselves about the 
philosophical comprehension of their sensuous experiences, 
and who do not strive after general knowledge, can promote 
science only in a very slight degree, and the chief value of 


their hard-won knowledge of details lies in the general 
results which more comprehensive minds will one day 
derive from them. 

From a general survey of the course of biological develop- 
ment since Linnseus' time, we can easily see, as Bar has 
pointed out, a continual vacillation between these two ten- 
dencies, at one time a prevalence of the empirical — the 
so-called exact — and then again of the philosophical or 
speculative tendency. Thus at the end of the last century, 
in opposition to Linnseus' purely empirical school, a natural- 
philosophical reaction took place, the moving spirits of 
which, Lamarck, Geoffrey St. Hilaire, Goethe, and Oken, 
endeavoured by their mental work to introduce light and 
order into the chaos of the accumulated empirical raw 
material. In opposition to the many errors and specu- 
lations of these natural philosophers, who went too far, 
Cuvier then came forward, introducing a second, purely 
empirical period. It reached its most one-sided development 
between the years 1830-1860, and there now followed a 
second philosophical reaction, caused by Darwin's work. 
Thus during the last ten years, men again have begun to 
endeavour to obtain a knowledge of the general laws of 
nature, to which, after all, all detailed knowledge of experi- 
ence serves only as a foundation, and through which alone 
it acquires its true value. It is through philosophy alone 
that natural knowledge becomes a true science, that is, 
a philosophy of nature. (Gen. Morph. i. 63-108.) 

Jean Lamarck and Wolfgang Goethe stand at the head of 
all the great philosophers of nature who first established a 
theory of organic development, and who are the illustrious 
fellow-workers of Darwin. I turn first to our beloved 


Goethe, who, among all, stands in the closest relations to us 
Germans. However, before I explain his special services 
to the theory of development, it seems to me necessary 
to say a few words about his importance as a naturalist in 
general, as it is commonly very little known. 

I am sure most of my readers honour Goethe only as a 
poet and a man ; only a few have any conception of the high 
value of his scientific works, and of the gigantic stride with 
which he advanced before his own age — advanced so much 
that most naturalists of that time were unable to follow 
him. In several passages of his scientific writings he 
bitterly complains of the narrow-mindedness of professed 
naturalists, who do not know how to value his works (who 
cannot see the wood for the trees), and who cannot rouse 
themselves to discover the general laws of nature among the 
mass of details. He is only too just when he utters the 
reproach — "The philosophers will very soon discover that 
observers rarely rise to a stand-point from which they can 
survey so many important objects." It is true, at the same 
time, that their want of appreciation was caused by the 
false road into which Goethe was led in his theory of colours. 

This theory of colours, which he himself designates as 
the favourite production of his leisure, however much 
that is beautiful it may contain, is a complete failure in 
regard to its foundations. The exact mathematical method 
by means of which alone it is possible, in inorganic 
sciences, but above all in physics, to raise a structure 
step by step on a thoroughly firm basis, was altogether re- 
pugnant to Goethe. In rejecting it he allowed himself not 
only to be very unjust towards the most eminent phy- 
sicists, but to be led into errors which have greatly injured 

VOL. I. G 


the fame of his other valuable works. It is quite different 
in the organic sciences, in which we are hut rarely able to 
proceed, from the beginning, upon a firm mathematical 
basis; we are rather compelled, by the infinitely difficult 
and intricate nature of the problem, at the first to form 
inductions — that is, we are obliged to endeavour to establish 
general laws by numerous individual observations, which 
are not quite complete. A comparison of kindred series of 
phenomena, or the method of combination, is here the most 
important instrument for inquiry, and this method was 
applied by Goethe with as much success as with conscious 
knowledge of its value, in his works relating to the 
philosophy of nature. 

The most celebrated among Goethe's writings relating to 
organic nature is his Metamorphosis of Plants, which ap- 
peared in 1790, a work which distinctly shows a grasp of the 
fundamental idea of the theory of development, inasmuch 
as Goethe, in it, was labouring to point out a single organ, 
by the infinitely varied development and metamorphosis of 
which the whole of the endless variety of forms in the world 
of plants might be conceived to have arisen; this funda- 
mental organ he found in the leaf. If at that time the mi- 
croscope had been generally employed, if Goethe had 
examined the structure of organisms by the means of the 
microscope, he would have gone still further, and would 
have seen that the leaf is itself a compound of individual 
parts of a lower order, that is, of cells. He would then not 
have declared that the leaf, but that the cell is the real fun- 
damental organ by the multiplication, transformation, and 
combination (synthesis) of which, in the first place, the leaf 
is formed ; and that, in the next place, by transformation, 


goethe's theory of the skull. 83 

variation, and combination of leaves there arise all the 
varied beauties in form and colour which we admire in the 
green parts, as well as in the organs of propagation, or the 
flowers of plants. Goethe here showed that in order to 
comprehend the whole of the phenomena, we must in the 
first place compare them, and, secondly, search for a simple 
type, a simple fundamental form, of which all other forms 
are only infinite variations. 

Something similar to what he had here done for the meta- 
morphosis of plants he then did for the Vertebrate 
animals, in his celebrated vertebral theory of the skull. 
Goethe was the first to show, independently of Oken, who 
almost simultaneously arrived at the same thought, that the 
skull of man and of all Vertebrate animals, in particular 
mammals, is nothing more than a bony case, formed of 
the same bones, — that is, vertebrae, — out of which the spine 
also is composed. The vertebrae of the skull are like those 
of the spine, bony rings lying behind each other, but in the 
skull are peculiarly changed and specialized (differentiated). 
Although this idea has been strongly modified by recent 
discoveries, yet in Goethe's day it was one of the greatest 
advances in comparative anatomy, and was not only one 
of the first advances towards the understanding of the 
structure of Vertebrate animals, but at the same time ex- 
plained many individual phenomena. When two parts of a 
body, such as the skull and spine, which appear at first 
ight so different, were proved to be parts originally the 
same, developed out of one and the same foundation, one of 
the difficult problems of the philosophy of nature was 
solved. Here again we meet the notion of a single type — 
the conception of a single principle, which becomes in- 


finitely varied in the different species, and in the parts of 
individual species. 

But Goethe did not merely endeavour to search for such 
far-reaching laws, he also occupied himself most actively 
for a long time with numerous individual researches, 
especially in comparative anatomy. Among these, none is 
perhaps more interesting than the discovery of the midjaiv- 
bone in man. As this is, in several respects, of importance 
to the theory of development, I shall briefly explain it 
here. There exist in all mammals two little bones in the 
upper jaw, which meet in the centre of the face, below the 
nose, and which he between the two halves of the real upper 
jawbone. These two bones, which hold the four upper 
cutting teeth, are recognized without difficulty in most 
mammals ; in man, however, they were at that time un- 
known, and celebrated comparative anatomists even laid 
great stress upon this want of a mid jawbone, as they con- 
sidered it to constitute the principal difference between men 
and apes — the want of a mid jawbone was, curiously 
enough, looked upon as the most human of all human 
characteristics. But Goethe could not accept the notion 
that man, who in all other corporeal respects was clearly 
only a mammal of higher development, should lack this mid 

By the general law of induction as to the mid jawbone 
he arrived at the special deductive conclusion that it must 
exist in man also, and Goethe did not rest until, after com- 
paring a great number of human skulls, he really found 
the mid jawbone. In some individuals it is preserved 
throughout a whole lifetime, but usually at an early age 
it coalesces with the neighbouring upper jawbone, and is 


therefore only to be found as an independent bone in very- 
youthful skulls. In human embryos it can now be pointed 
out at any moment. In man, therefore, the mid jawbone 
actually exists, and to Goethe the honour is due of having 
first firmly established this fact, so important in many 
respects ; and this he did while opposed by the celebrated 
anatomist, Peter Camper, one of the most important pro- 
fessional authorities. The way by which Goethe succeeded 
in establishing this fact is especially interesting ; it is the 
way by which we continually advance in biological science, 
namely, by way of induction and deduction. Induction 
is the inference of a general law from the observation of 
numerous individual cases ; deduction, on the other hand, 
is an inference from this general law a applied to a single case 
which has not yet been actually observed. From the col- 
lected empirical knowledge of those days, the inductive 
conclusion was arrived at that all mammals had mid jaw- 
bones. Goethe drew from this the deductive conclusion, 
that man, whose organization was in all other respects not 
essentially different from mammals, must also possess this 
mid jawbone; and on close examination it was actually 
found. The deductive conclusion was confirmed and verified 
by experience. 

Even these few remarks may serve to show the great 
value which we must ascribe to Goethe's biological re- 
searches. Unfortunately most of his labours devoted to 
this subject are so hidden in his collected works, and his 
most important observations and remarks so scattered in 
numerous individual treatises — devoted to other subjects — 
that it is difficult to find them out. It also sometimes 
happens that an excellent, truly scientific remark is so 
I. 4- 


much interwoven with a mass of useless philosophical 
fancies, that the latter greatly detract from the former. 

Nothing is perhaps more characteristic of the extraordi- 
nary interest which Goethe took in the investigation of 
organic nature than the lively way in which, even in his 
last years, he followed the dispute which broke out in 
France between Cuvier and Geoffrey de St. Hilaire. Goethe, 
in a special treatise which was only finished a few days 
before his death, in March, 1832, has given an interesting 
description of this remarkable dispute and its general im- 
portance, as well as an excellent sketch of the two great 
opponents. This treatise bears the title "Principes de 
Philosophie Zoologique par M. Geoffroy de Saint Hilaire " ; 
it is Goethe's last work, and forms the conclusion of the 
collected edition of his works. The dispute itself was, in 
several respects, of the highest interest. It turned essentially 
upon the justification of the theory of development. It 
was carried on, moreover, in the bosom of the French 
Academy, by both opponents, with a personal vehemence 
almost unheard of in the dignified sessions of that learned 
body ; this proved that both naturalists were fighting for 
their most sacred and deepest convictions. The conflict 
began on the 22nd of February, and was followed by 
several others ; the fiercest took place on the 19th of 
July, 1830. Geoffroy, as the chief of the French nature- 
philosophers, represented the theory of natural development 
and the monistic conception of nature. He maintained the 
mutability of organic species, the common descent of the 
individual species from common primary forms, and the 
unity of their organization — or the unity of the plan of 
structure, as it was then called. 


Cuvier was the most decided opponent of these views, 
and according to what we have seen, it could not be 
otherwise. He endeavoured to show that the nature- 
philosophers had no right to rear such comprehensive con- 
clusions on the basis of the empirical knowledge then 
possessed, and that the unity of organization — or plan of 
structure of organisms — as maintained by them, did not 
exist. He represented the teleological (dualistic) concep- 
tion of nature, and maintained that "the immutability of 
species was a necessary condition for the existence of a 
scientific history of nature." Cuvier had the great advan- 
tage over his opponent, that he was able to bring towards 
the proof of his assertions things obvious to the eye ; these, 
however, were only individual facts taken out of their con- 
nection with others. Geoffroy was not able to prove the 
higher and general connection of individual phenomena 
which he maintained, by equally tangible details. Hence 
Cuvier, in the eyes of the majority- gained the victory, and 
decided the defeat of the nature-philosophy and the 
supremacy of the strictly empiric tendency for the next 
thirty years. 

Goethe of course supported Geoffroy's views. How deeply 
interested he was, even in his 81st year, in this great contest 
is proved by the following anecdote related by Soret : — 

"Monday, Aug. 2nd, 1830. — The news of the outbreak of 
the revolution of July arrived in Weimar to-day, and has 
caused general excitement. In the course of the afternoon 
I went to Goethe. ' Well ? ' he exclaimed as I entered, 
' what do you think of this great event ? The volcano has 
burst forth, all is in flames, and there are no more negotia- 
tions behind closed doors.' ' A dreadful affair,' I answered ; 


' but what else could be expected under the circum- 
stances, and with such a ministry, except that it would 
end in the expulsion of the present royal family ? ' ' We do 
not seem to understand each other, my dear friend,' replied 
Goethe. ' I am not speaking of those people at all ; I am 
interested in something very different, I mean the dispute 
between Cuvier and Geoffroy de Saint Hilaire, which has 
broken out in the Academy, and which is of such great im- 
portance to science.' This remark of Goethe's came upon 
me so unexpectedly, that I did not know what to say, and 
my thoughts for some minutes seemed to have come to a 
complete standstill. ' The affair is of the utmost import- 
ance,' he continued, ' and you cannot form any idea of what 
I felt on receiving the news of the meeting on the 19th. 
In Geoffroy de Saint Hilaire we have now a mighty ally 
for a long time to come. But I see also how great the 
sympathy of the French scientific world must be in this 
affair, for, in spite of the terrible political excitement, the 
meeting on the 19th was attended by a full house. The 
best of it is, however, that the synthetic treatment of 
nature, introduced into France by Geoffroy, can now no 
longer be stopped. This matter has now become public 
through the discussions in the Academy, carried on in the 
presence of a large audience; it can no longer be referred 
to secret committees, or be settled or suppressed behind 
closed doors.' " 

In my book on " The General Morphology of Organisms " 
I have placed as headings to the different books and chapters 
a selection of the numerous interesting and important sen- 
tences in which Goethe clearly expresses his view of 
organic nature and its constant development. I will here 


quote a passage from the poem entitled, "The Metamor- 
phosis of Animals " (1819). 

" All members develop themselves according to eternal laws, 
And the rarest form mysteriously preserves the primitive type. 
Form therefore determines the animal's way of life, 
And in turn the way of life powerfully reacts upon all form. 
Thus the orderly growth of form is seen to hold 
Whilst yielding to change from externally acting causes." * 

Here, clearly enough, the contrast between two different 
organic constructive forms is intimated, which are opposed 
to one another, and which by their inter-action determine 
the form of the organism ; on the one hand, a common inner 
original type, firmly maintaining itself, constitutes the 
foundation of the most different forms ; on the other hand, 
the externally active influence of surroundings and mode of 
life, which influence the original type and transform it. 
This contrast is still more definitely pointed out in the 
following passage : — 

" An inner original community forms the foundation of all 
organization ; the variety of forms, on the other hand, arises 
from the necessary relations to the outer world, and we 
may therefore justly assume an original difference of condi- 
tions, together with an uninterruptedly progressive trans- 
formation, in order to be able to comprehend the constancy 
as well as the variations of the phenomena of form." 

The " original type " which constitutes the foundation of 

* Alle Glieder bilden sich aus nach ew'gen Gesetzen, 
End die seltenste Form bewahrt im Geheimniss das Urbild. 
Also bestimmt die Gestalt die Lebensweise des Thieres. 
Und die Weise zu leben, sie wirkt auf alle Gestalten 
Machtig zuriick. So zeiget sich fest die geordnete Bildung, 
Welche zum Wechsel sich neigt durch ausserlich wirkende Wesen. 


every organic form " as the inner original community " is 
the inner constructive force, which receives the original 
direction of form-production — that is, the tendency to give 
rise to a particular form — and is propagated by Inheritance. 
The "uninterruptedly progressive transformation," on the 
other hand, which " springs from the necessary relations to 
the outer world," acting as an external formative force, 
produces, by Adaptation to the surrounding conditions of 
life, the "infinite variety of forms" (Gen. Morph. i. 154; 
ii. 224). The internal formative tendency of Inheritance, 
which retains the unity of the original type, is called by 
Goethe in another passage the centripetal force of the organ- 
ism, or its tendency to specification ; in contrast with this he 
calls the external formative tendency of Adaptation, which 
produces^ the variety of organic forms, the centrifugal force 
of organisms, or their tendency to variation. The passage 
in which he clearly indicates the " equilibrium " of these two 
extremely important organic formative tendencies, runs as 
follows : " The idea of metamorphosis resembles the vis 
centrifuga, and would lose itself in the infinite, if a counter- 
poise were not added to it : I mean the tendency to specifi- 
cation, the strong power to preserve what once has come 
into being, a vis centripeta, which in its deepest foundation 
cannot be affected by anything external." 

Metamorphosis, according to Goethe, consists not merely, 
as the word is now generally understood, in the changes of 
form which the organic individual experiences during its 
individual development, but, in a wider sense, in the 
transformation of organic forms in general. His idea of 
metamorphosis is almost synonymous with the theory of 
development. This is clear, among other things, from the 


following passage : — " The triumph of physiological meta- 
morphosis manifests itself where the whole separates and 
transforms itself into families, the families into genera, the 
genera into species, and then again into other varieties 
down to the individual. This operation of nature goes on 
ad infinitum ; she cannot rest inactive, but neither can she 
keep and preserve all that she has produced. From seeds 
there are always developed varying plants, exhibiting the 
relations of their parts to one another in an altered manner." 

Goethe had, in truth, discovered two great mechanical 
forces of nature, which are the active causes of organic 
formations, his two organic formative tendencies — on the 
one hand the conservative, centripetal, and internal forma- 
tive tendency of Inheritance or specification ; and on the 
other hand the progressive, centrifugal, and external form- 
ative tendency of Adaptation, or metamorphosis. This 
profound biological intuition could not but lead him natur- 
ally to the fundamental idea of the Doctrine of Filiation, that 
is, to the conception that the organic species resembling one 
another in form are actually related by blood, and that they 
are descended from a common orignal type. In regard to 
the most important of all animal groups, namely that of 
Vertebrate animals, Goethe expresses this doctrine in the 
following passage (1796) : — " Thus much then we have 
gained, that we may assert without hesitation that all the 
more perfect organic natures, such as fishes, amphibious 
animals, birds, mammals, and man at the head of the last, 
were all formed upon one original type, which only varies 
more or less in pails which are none the less permanent, and 
still daily changes and modifies its form by propagation." 

This sentence is of interest in more than one way. The 


theory that all " the more perfect organic natures," that is 
all Vertebrate animals, are descended from one common 
prototype, that they have arisen from it by propagation 
(Inheritance) and transformation (Adaptation), may be 
distinctly inferred. But it is especially interesting to 
observe that Goethe admits no exceptional position for man, 
but rather expressly includes him in the tribe of the other 
Vertebrate animals. The most important special inference 
of the Doctrine of Filiation, that man is descended from 
other Vertebrate animals, may here be recognized in the 
germ. 3 

This exceedingly important fundamental idea is expressed 
by Goethe still more clearly in another passage (1807), in 
the following words : — " If we consider plants and animals in 
their most imperfect condition, they can scarcely be distin- 
guished. But this much we can say, that the creatures 
which by degrees emerge as plants and animals out of a 
common phase, where they are barely distinguishable, arrive 
at perfection in two opposite directions ; so that the plant in 
the end reaches its highest glory in the tree, which is 
immovable and stiff, the animal in man, who possesses 
the greatest elasticity and freedom." This remarkable 
passage not only indicates most explicitly the genealogical 
relationship between the vegetable and animal kingdoms, 
but contains the germ of the monophyletic hypothesis of 
descent, the importance of which I shall have to explain 
hereafter. (Compare Chapter XVI. and the Pedigree, vol. ii. 
pp. 74, 75.) 

At the time when Goethe in this way sketched the 
fundamental features of the Theory of Descent, another 
German philosopher, Gottfried Reinhold Treviranus, of 


Bremen (born 1776, died 1837), was zealously engaged at 
the same work. As Wilhelm Focke has recently shown, 
Treviranus, even in the earliest of his greater works, " The 
Biology or Philosophy of Animate Nature," which appeared 
at the beginning of the present century, had already 
developed monistic views of the unity of nature, and of the 
genealogical connection of the species of organisms, which 
entirely correspond with our present view of the matter. In 
the first three* volumes of the Biology, which appeared succes- 
sively in 1802, 1803, and 1805 (therefore several years before 
Oken's and Lamarck's principal works), we find numerous 
passages which are of interest in this respect. I shall here 
quote only a few of the most important. 

In speaking of the principal question of our theory, the 
question of the origin of organic species, Treviranus makes 
the following remarks : — " Every form of life can be 
produced by physical forces in one of two ways : either by 
coming into being out of formless matter, or by modification 
of an already existing form by a continued process of 
shaping. In the latter case the cause of this modification 
may lie either in the influence of a dissimilar male genera- 
tive matter upon the female germ, or in the influence of 
other powers which operate only after procreation. In every 
living being there exists the capability of an endless variety 
of form-assumption ; each possesses the power to adapt its 
organization to the changes of the outer world, and it is this 
power put into action by the change of the universe that 
has raised the simple zoophytes of the primitive world to 
continually higher stages of organization, and has introduced 
a countless variety of species into animate nature." 

By zoophytes, Treviranus here means organisms of th& 


lowest order and of the simplest character, namely, those 
neutral primitive beings which stand midway between 
animals and plants, and on the whole correspond with our 
protista. " These zoophytes," he remarks in another pass- 
age, "are the original forms out of which all the organisms 
of the higher classes have arisen by gradual development. 
We are further of opinion that every species, as well as 
•every individual, has certain periods of growth, of bloom, 
and of decay, but that the decay of a species is degeneration, 
not dissolution, as in the case of the individual. From this it 
appears to us to follow that it was not the great catastrophies 
of the earth' (as is generally supposed) which destroyed the 
animals of the primitive world, but that many survived 
them, and it is more probable that they have disappeared 
from existing nature, because the species to which they 
belonged have completed the circle of their existence, and 
have become changed into other kinds." 

When Treviranus, in this and other passages, points to 
•degeneration as the most important cause of the transforma- 
tion of the animal and vegetable species, he does not under- 
stand by it what is now commonly called degeneration. 
With him " degeneration " is exactly what we now call 
Adaptation or modification, by the action of external 
formative forces. That Treviranus explained this trans- 
transformation of organic species by Adaptation, and its 
preservation by Inheritance, and thus the whole variety of 
organic forms by the inter-action of Adaptation and In- 
heritance, is clear also from several other passages. How 
profoundly he grasped the mutual dependence of all living 
creatures on one another, and in general the universal 
connection betiveen cause and effect — that is, the monistic 


■causal connection between all members and parts of the 
universe — is further shown, among others, by the following 
remarks in his Biology : — " The living individual is depen- 
dent upon the species, the species upon the fauna, the fauna 
upon the whole of animate nature, and the latter upon the 
organism of the earth. The individual possesses indeed a 
peculiar life, and so far forms its own world. But just 
because its life is limited it constitutes at the same time an 
organ in the general organism. Every living body exists in 
consequence of the universe, but the universe, on the other 
hand, exists in consequence of it." 

It is self-evident that so profound and clear a thinker as 
Treviranus, in accordance with this grand mechanical con- 
ception of the universe, could not admit for man a privileged 
and exceptional position in nature, but assumed his gradual 
development from lower animal forms. And it is equallv 
self-evident, on the other hand, that he did not admit a 
chasm between organic and inorganic nature, but main- 
tained the absolute unity of the organization of the whole 
universe. This is specially attested by the following 
sentence : — " Every inquiry into the influence of the whole 
of nature on the living world must start from the principle, 
that all living forms are products of physical influences, 
which are acting even now, and are changed only in degree, 
or in their direction." Hereby, as Treviranus himself says, 
" The fundamental problem of biology is solved," and we 
add, solved in a purely mechanical or monistic sense. 

Neither Treviranus nor Goethe is commonly considered 
the most eminent of the German nature-philosophers, but 
Lorenz Oken, who, in establishing the vertebral theory of the 
skull, came forward as a rival to Goethe, and did not 


entertain a very kindly feeling towards him. Although they 
lived for some time in the same neighbourhood, yet the 
natures of these two men were so very different, that they 
could not well be drawn towards each other. Oken's " Manual 
of the Philosophy of Nature," which may be designated as the 
most important production of the nature-philosophy school 
then existing in Germany, appeared in 1809, the same year 
in which Lamarck's fundamental work, the " Philosophie 
Zoologique-," was published. As early as 1802, Oken had 
published an " Outline of the Philosophy of Nature." As we 
have already intimated, in Oken's as in Goethe's works, a 
number of valuable and profound thoughts are hidden 
among a mass of erroneous, very eccentric, and fantastic con- 
ceptions. Some of these ideas have only quite recently and 
gradually become recognized in science, many years after 
they were first expressed. I shall here quote only two 
thoughts, which are almost prophetic, and which at the 
same time stand in the closest relation to the theory of 

One of the most important of Oken's theories, which was 
formerly very much decried, and was most strongly com- 
batted, especially by the so-called " exact experimentalists," 
is the idea that the phenomena of life in all organisms pro- 
ceed from a common chemical substance, so to say, from a 
general simple vital-substance, which he designated by the 
name Urschleim, or original slime. By it he meant, as the 
name indicates, a mucilaginous substance, an albuminous 
combination, which exists in a semi-fluid condition of aggre- 
gation, and possesses the power, by adaptation to different 
conditions of existence in the outer world and by inter- 
action with its material, of producing the most various forms. 

oxen's theoeies. 97 

Now, we need only change the expression "original slime" 
(Urschleim) into Protoplasm, or cell-substance, in order to 
arrive at one of the grandest results which we owe to 
microscopic investigations during the last ten years, more 
especially to those of Max Schultze. By these investigations 
it has been shown that in all living bodies, without ex- 
ception, there exists a certain quantity of mucilaginous albu- 
minous matter, in a semi-fluid condition; and that this 
nitrogen-holding carbon-compound is exclusively the ori- 
ginal seat and agent of all the phenomena of life, and of 
all production of organic forms. All other substances which 
appear in the organism, besides these, are either formed by 
this active matter of life, or have been introduced from with- 
out. The organic egg, the original cell out of which every 
animal and plant is first developed, consists essentially only 
of one round little lump of such albuminous matter. Even 
the yolk of an egg is nothing but albumen, mixed with 
granules of fat. Oken was therefore right when, more 
divining than knowing, he made the assertion — "Every 
organic thing has arisen out of slime, and is nothing but 
slime in different forms. This primitive slime originated 
in the sea, from inorganic matter in the course of planetary- 

Another equally grand idea of the same philosopher is 
closely connected with his theory of primitive slime, which 
coincides with the extremely important Protoplasm theory 
For Oken, as early as 1809, asserted that the primitive 
slime produced in the sea by spontaneous generation, at 
once assumed the form of microscopically small bladders, 
which he called "Mile" or "Infusoria? "Organic nature 
has for its basis an infinity of such vesicles." These little 

VOL. I. H 


bladders arise from original semi-fluid globules of the primi- 
tive slime, by the fact of their periphery becoming con- 
densed. The simplest organism, as well as every animal and 
every plant of higher kind, is nothing else than " an accu- 
mulation (synthesis) of such infusorial bladders, which 
by various combinations assume various forms, and thus 
develop into higher organisms." Here again we need only 
translate the expression little bladder, or infusorium, by the 
word cell, and we arrive at the Cell theory, one of the 
grandest biological theories of our century. Schleiden and 
Schwann, about thirty years ago, were the first to furnish 
experiential proof that all organisms are either simple cells, 
or accumulations (syntheses) of such cells, and the more recent 
protoplasm theory has shown that protoplasm (the original 
slime) is the most essential (and sometimes the only) con- 
stituent part of the genuine cell. The properties which Oken 
ascribes to his Infusoria are exactly the properties of cells, 
the properties of elementary beings, by whose accumulation, 
combination, and varying development, the higher organisms 
are formed. 

These two extremely fruitful thoughts of Oken, on account 
of the absurd form in which he expressed them, were at 
first little heeded, or entirely misunderstood, and it was re- 
served for a much later era to establish them by actual 
observation. The supposition that the individual species of 
plants and animals originated from common prototypes by 
a slow and gradual development of the higher organisms out 
of lower ones, was of course most closely connected with 
these ideas. Man's descent from lower organisms was like- 
wise asserted by Oken — " Man has been developed, not 
created." Although many arbitrary perversities and ex- 


travagant fancies may be found in Oken's philosophy of 
nature, they must not prevent us paying our just admira- 
tion to these grand ideas, which were so far in advance of 
their age. This much is clearly evident from the statements 
of Goethe and Oken which we have quoted, and from the 
views of Lamarck and Geofrroy which have to be discussed 
next, that during the first decade of our century no 
doctrine approached so nearly to the natural Theory of 
Descent, newly established by Darwin, as the much decried 
" Natur-philosophie." 




Kant's Dualistic Biology. — His Conception of the Origin of Inorganic 
Nature by Mechanical Causes, of Organic Nature by Causes acting for a 
Definite Purpose. — Contradiction of this Conception with his leaning 
towards the Theory of Descent. — Kant's Genealogical Theory of 
Development. — Its Limitation by his Teleology. — Comparison of 
Genealogical Biology with Comparative Philology. — Views in favour of 
the Theory of Descent entertained by Leopold Bueh, Bar, Schleiden, 
Unger, Schaafhausen, Victor Carus, Biichner. — French Nature, 
philosophy. — Lamarck's Philosophie Zoologique. — Lamarck's Monistic 
(mechanical) System of Nature. — His Views of the Inter-action of the 
Two Organic Formative Tendencies of Inheritance and Adaptation. — 
Lamarck's Conception of Man's Development from Ape-like Mammals. — 
Geoffroy St. Hilaire's, Naudin's, and Lecoq's Defence of the Theory of 
Descent. — English Nature-philosophy. — Views in favour of the Theory 
of Descent, entertained by Erasmus Darwin, W. Herbert, Grant, Freke, 
Herbert Spencer, Hooker, Huxley. — The Double Merit of Charles 

The teleological view of nature, which explains the phe- 
nomena of the organic world by the action of a personal 
Creator acting for a definite purpose, necessarily leads, when 
carried to its extreme consequences, either to utterly unten- 
able contradictions, or to a twofold (dualistic) conception 
of nature, which most directly contradicts the unity and 
simplicity of the supreme laws which are everywhere 
perceptible. The philosophers who embrace teleology must 

kant's biological theories. ioi 

necessarily assume two fundamentally different natures : 
an inorganic nature, which must be explained by causes 
acting mechanically (causae efficientes), and an organic 
nature, which must be explained by causes acting for a 
definite purpose (causse finales). (Compare p. 34.) 

This dualism meets us in a striking manner when con- 
sidering the conceptions of nature formed by Kant, one of 
the greatest German philosophers, and his ideas of the com- 
ing into being of organisms. A closer examination of these 
ideas is forced upon us here, because in Kant we honour one 
of the few philosophers who combine a solid scientific cul- 
ture with an extraordinary clearness and profundity of 
speculation. The Konigsberg philosopher gained the highest 
celebrity, not only among speculative philosophers as the 
founder of critical philosophy, but acquired a brilliant name 
also among naturalists by his mechanical cosmogeny. Even 
in the year 1755, in his " General History of Nature, and 
Theory of the Heavens," 22 he made the bold attempt " to 
discuss the constitution and the mechanical origin of the 
whole universe, according to Newton's principles," and to 
•explain them mechanically by the natural course of develop- 
ment, to the exclusion of all miracles. This cosmogeny of 
Kant, or " cosmological gas theory," which we shall briefly 
discuss in a future chapter, was at a later day fully estab- 
lished by the French mathematician Laplace and the Eng- 
lish astronomer Herschel, and enjoys at the present day 
almost universal recognition. On account of this import- 
ant work alone, in which exact knowledge is coupled 
with most profound speculation, Kant deserves the honour- 
able name of a natural philosopher in the best and purest 
sense of the word. 


If we read Kant's Criticism of the Teleological Faculty 
of Judgment, his most important biological work, we 
perceive that in contemplating organic nature he always 
maintains what is essentially the teleological or dualistic 
point of view ; whilst for inorganic nature he, uncondition- 
ally and without reserve, assumes the mechanical or monis- 
tic method of explanation. He affirms that in the domain 
of inorganic nature all the phenomena can be explained by 
mechanical causes, by the moving forces of matter itself, but 
not so in the domain of organic nature. In the whole of 
Anorganology (in Geology and Mineralogy, in Meteorology 
and Astronomy, in the physics and chemistry of inorganic 
natural bodies), all phenomena are said to be explicable 
merely by mechanism (causa efficiens), without the interven- 
tion of a final purpose. In the whole domain of Biology, on 
the other hand — in Botany, Zoology, and Anthropology — me- 
chanism is not considered sufficient to explain to us all their 
phenomena ; but we are supposed to be able to comprehend 
them only by an assumption of & final cause acting for a defi- 
nite purpose (causa finalis). In several passages Kant em- 
phatically remarks that, from a strictly scientific point of 
view, all phenomena, without exception, require a mechani-' 
cal interpretation, and that mechanism alone can offer a true 
explanation. But at the same time he thinks, that in regard 
to living natural bodies, animals and plants, our human 
power of comprehension is limited, and not sufficient for 
arriving at the real cause of organic processes, especially at 
the origin of organic forms. The right of human reason to< 
explain all phenomena mechanically is unlimited, he says, 
but its poiver is limited by the fact that organic nature can 
be conceived only from a teleological point of view. 

rant's biological theoeies. 103 

Some passages are, however, very remarkable, in which 
Kant in a surprising manner deviates from this mode of 
viewing things, and expresses, more or less distinctly, the 
fundamental idea of the Theory of Descent. He even as- 
serts the necessity of a genealogical conception of the series 
of organisms, if we at all wish to understand it scien- 
tifically. The most important and remarkable of these pas- 
sages occurs in his " Methodical System of the Teleological 
Faculty of Judgment " (§ 79), which appeared in 1790 in the 
" Criticism of the Faculty of Judgment." Considering the 
extraordinary interest which this passage possesses, both for 
forming a correct estimate of Kant's philosophy, as well as 
for the Theory of Descent, I shall here insert it verbatim. 

" It is desirable to examine the great domain of organized 
nature by means of a methodical comparative anatomy, in 
order to discover whether we may not find in it something 
resembling a system, and that too in connection with the 
mode of generation, so that we may no longer be compelled 
to stop short with a mere consideration of forms as they are 
— which gives us no insight into their generation — and need 
no longer give up in despair all hope of gaining a full insight 
into this department of nature. The agreement of so many 
kinds of animals in a certain common plan of structure, which 
seems to be visible not only in their skeletons, but also in the 
arrangement of the remaining parts — so that a wonderfully 
simple typical form, by the shortening and lengthening of 
some parts, and by the suppression and development of 
others, might be able to produce an immense variety of 
species — gives us a ray of hope, though feeble, that here 
perhaps some result may be obtained, by the application of 
the principle of the mechanism of nature, without which, 


in fact, no science can exist. This analogy of forms (in so 
far as they seem to have been produced in accordance with 
a common prototype, notwithstanding their great variety) 
strengthens the supposition that they have an actual blood- 
relationship, due to origination from a common parent; a 
supposition which is arrived at by observation of the 
graduated approximation of one class of animals to another, 
beginning with the one in which the principle of purposive- 
ness seems to be most conspicuous, that is man, and extend- 
ing down to the polyps, and from these even down to mosses 
and lichens, and arriving finally at raw matter, the lowest 
stage of nature observable by us. From this matter and 
its forces the whole apparatus of Nature seems to have 
descended according to mechanical laws (such as those 
which she follows in the production of crystals) ; yet this 
apparatus, as seen in organic beings, is so incomprehensible 
to us, that we feel ourselves compelled to conceive for it a 
different principle. But it would seem that the archaeologist 
of Nature is at liberty to regard the great Family of 
creatures (for as a Family we must conceive it, if the above- 
mentioned continuous and connected relationship has a real 
foundation) as having sprung from the immediate results of 
her earliest revolutions, judging from all the laws of their 
mechanism known to or conjectured by him." 

If we take this remarkable passage out of Kant's 
" Criticism of the Teleological Faculty of Judgment," and 
consider it by itself, we cannot but be astonished to find 
how profoundly and clearly the great thinker, even in 1790, 
had recognized the inevitable necessity of the Doctrine 
of Descent, and designated it as the only possible way of 
explaining organic nature by mechanical laws — that is, by 


true scientific reasoning. On account of this one passage 
taken by itself, we might place Kant beside Goethe and 
Lamarck, as one of the first founders of the Doctrine of 
Descent ; and considering the high authority which Kant's 
Critical Philosophy most justly enjoys, this circumstance 
might perhaps induce many a philosopher to decide in 
favour of the theory. But as soon as we consider this 
passage in connection with the other train of thoughts in 
the "Criticism of the Faculty of Judgment," and balance 
it against other directly contradictory passages, we see 
clearly that Kant, in these and some similar (but weaker) 
sentences, went beyond himself, and abandoned the teleo- 
logical point of view which he usually adopts in Biology. 

Directly after the admirable passage which I have just 
quoted, there follows a remark which completely takes off 
its edge. After having quite correctly maintained the 
origin of organic forms out of raw matter by mechanical 
laws (in the manner of crystallization), as well as a gradual 
development of the different species by descent from one 
common original parent, Kant adds, " But he (the archseolo- 
gist of nature, that is the palaeontologist) must for this end 
ascribe to the common mother an organization ordained 
purposely with a view to the needs of all her offspring, 
•otherwise the possibility of suitability of form in the pro- 
ducts of the animal and vegetable kingdoms (i.e. teleological 
adaptation) cannot be conceived at all." This addition 
clearly contradicts the most important fundamental thought 
of the preceding passage, viz. that a purely mechanical ex- 
planation of organic nature becomes possible through the 
Theory of Descent. And that the teleological conception 
of organic nature predominated with Kant, is shown by 


the heading of the remarkable § 79, which contains the two- 
contradictory passages cited : " Of the Necessary Subordina- 
tion of the Mechanical to the Teleological Principle, in the 
explanation of a thing as a purpose or object of Nature." 

He expresses'himself most decidedly against the mechanical 
explanation of organic nature in the following passage 
(§ 74) : "It is quite certain that we cannot become sufficiently 
acquainted with organized creatures and their hidden 
potentialities by aid of purely mechanical natural principles,. 
much less can we explain them ; and this is so certain, that 
we may boldly assert that it is absurd for man even to con- 
ceive such an idea, or to hope that a Newton may one day 
arise able to make the production of a blade of grass com- 
prehensible, according to natural laws ordained by no inten- 
tion; such an insight we must absolutely deny to man." 
Now, however, this impossible Newton has really appeared 
seventy years later in Darwin, whose Theory of Selection 
has actually solved the problem, the solution of which 
Kant had considered absolutely inconceivable ! 

In connection with Kant and the German philosophers- 
■whose theories of development have already occupied us in 
the preceding chapter, it seems justifiable to consider briefly 
some other German naturalists and philosophers, who, in the 
course of our century, have more or less distinctly resisted 
the prevailing teleological views of creation, and vindicated 
the mechanical conception of things which is the basis of 
the Doctrine of Filiation. Sometimes general philosophical 
considerations, sometimes special empirical observations, 
were the motives which led these thinking men to form the 
idea that the various individual species of organisms must 
have originated from common primary forms. Among them 


I must first mention the great German geologist, Leopold 
Buch. Important observations as to the geographical dis- 
tribution of plants led him to the following remarkable 
assertion in his excellent "Physical Description of the 
Canary Islands " : — 

"The individuals of genera* on continents, spread and 
widely diffuse themselves, and by the difference of localities,, 
nourishment, and soil, form varieties ; and being in conse- 
quence of their isolation never crossed by other varieties, 
and so brought back to the main type, they in the end 
become a permanent and a distinct species. Then, perhaps, 
in other ways, they once more become associated with other 
descendants of the original form — which have likewise 
become new varieties — and both now appear as very distinct 
species, no longer mingling with one another. Not so on 
islands. Being commonly confined in narrow valleys or 
within the limit of small zones, individuals can reach one 
another and destroy every commencing production of a per- 
manent variety. Much in the same way the peculiarities or 
faults in language, originating with the head of some family, 
become, through the extension of the family, indigenous 
throughout a whole district. Lf the district is separated and 
isolated, and if the language is not brought back to its- 
former purity by constant connection with that spoken in 
neighbouring districts, a dialect will be the result. If natural 
obstacles, forests, constitution, form of government, unite 
the inhabitants of the separate district still more closely, 
and separate them still more completely from their neigh- 
bours, the dialect is fixed, and becomes a completely 
distinct language." (Uebersicht der Flora auf clen Canarien, 
S. 133.) 


We perceive that Buch is here led to the fundamental 
idea of the Theory of Descent by the phenomena of the 
geography of plants, a department of biological knowledge 
which in fact furnishes a mass of proofs in favour of it. 
Darwin has minutely discussed these proofs in two separate 
chapters of his book (the 11th and 12th). Bach's remark is 
further of interest, because it leads us to the exceedingly 
instructive comparison of the different branches of language 
with the species of organisms, a comparison which is of the 
greatest use to Comparative Philology, as well as to Compara- 
tive Botany and Zoology. Just as, for example, the different 
dialects, provincialisms, branches, and off-shoots of the 
German, Slavonic, Greco-Latin, and Irano-Indian parent lan- 
guage, are derived from a single common Indo- Germanic 
parent tongue, and just as their differences are explained by 
Adaptation, and their common fundamental characters ex- 
plained by Inheritance, so in like manner the different species, 
genera, families, orders, and classes of Vertebrate animals 
are derived from a single common vertebrate form of animal. 
Here also Adaptation is the cause of differences, Inheritance 
the cause of community of character. This interesting 
parallelism in the divergent development of the forms of 
speech and the forms of organisms has been discussed in 
the clearest manner by one of our first comparative philolo- 
gists, the talented Augustus Schleicher, whose premature 
death, four years ago, remains an irreparable loss, not only 
to our University of Jena, but to the whole of monistic 
science. 6 

Among other eminent German naturalists who have ex- 
pressed their belief in the Theory of Descent more or less 
-distinctly, arriving at their conclusion in very various ways, 


I must next mention Carl Ernst Bar, the great reformer of 
animal embryology. In a lecture delivered in 1834, entitled 
" The Most General Laws of Nature in All Development," 
he shows, in the clearest way, that only in a very childish 
view of nature could organic species he regarded as perma- 
nent and unchangeable types, and that really they can be 
only passing series of generations, which have developed by 
transformation from a common original form. The same 
conception again received firm support from Baer, in 1859, 
through a consideration of the of laws the geographical 
distribution of organisms. 

J. M. Schleiden, who founded, thirty years ago, in Jena, a 
new epoch in Botany by his strictly empirico-philosophical 
and truly scientific method, illustrated the philosophical 
significance of the conception of organic species in his inci- 
sive " Outlines of Scientific Botany," 7 and showed that it 
had only a subjective origin in the general law of specifica- 
tion. The different species of plants are only the specified 
productions of the formative tendencies of plants, which arise 
from the various combinations of the fundamental forces of 
organic matter. 

The eminent botanist, F. Unger, of Vienna, was led by 
his profound and comprehensive investigations on extinct 
vegetable species, to a palaeontological history of the de- 
velopment of the vegetable kingdom, which distinctly asserts 
the principle of the Theory of Descent. In his " Attempt at 
a History of the World of Plants" (1852), he maintains the 
derivation of all different species of plants from a few 
primary forms, and perhaps from a single original plant, a 
simple vegetable cell. He shows that this view is founded 
on the genetic connection of all vegetable forms, and is 


necessary, not merely upon philosophical grounds, but upon 
those of experience and observation. 8 

Victor Carus, of Leipzig, in the Introduction to his 
excellent "System of Animal Morphology," 9 published in 
1853, in which he endeavours to establish in a philosophical 
manner the universal constructive laws of the animal body 
through comparative anatomy and the history of develop- 
ment, makes the following remark : — " The organisms buried 
in the most ancient geological strata must be looked upon 
as the ancestors from whom the rich diversity of forms of 
the present creation have originated by continued genera- 
tion, and by accommodation to progressive and very different 
conditions of life." 

In the same year (1853) Schaaffhausen, the anthropologist 
of Bonn, in an Essay " On the Permanence and Transforma- 
tion of Species," declared himself decidedly in favour of the 
Theory of Descent. According to him, the living species of 
animals and plants are the transformed descendants of ex- 
tinct species, from which they have arisen by gradual modi- 
fication The divergence or separation of the most nearly 
allied species takes place by the destruction of the connect- 
ing intermediate stages. Schaaffhausen also maintained, 
with distinctness, the origin of the human race from ani- 
mals, and its gradual development from ape-hke animals, the 
most important deduction from the Doctrine of Filiation. 

Lastly, we have still to mention among the German Nature- 
philosophers the name of Louis Biichner, who, in his cele- 
brated work, "Force and Matter" (1855), also independently 
developed the principles of the Theory of Descent, taking 
his stand mainly on the ground of the undeniable evidences 
of fact which are furnished by the pakeontological and in- 

lamarck's philosophy. i i r 

dividual development of organisms, as well as by their com- 
parative anatomy and by the parallelism of these series of 
development. Blichner showed very clearly that, even from 
such data alone, the derivation of the different organic 
species from common primary forms followed as a necessary 
conclusion, and that the origin of these original primary 
forms could only be conceived of as the result of a sponta- 
neous generation. 

We now turn from the German to the French Nature- 
philosophers, who have likewise held the Theory of Descent, 
since the beginning of the present century. At their head 
stands Jean Lamarck, who occupies the first place next 
to Darwin and Goethe in the history of the Doctrine of 
Filiation. To him will always belong the immortal glory of 
having for the first time worked out the Theory of Descent, 
as an independent scientific theory of the first order, and as 
the philosophical foundation of the whole science of Biology. 
Although Lamarck was born as early as 1744, he did not 
begin the publication of his theory until the commence- 
ment of the present century, in 1801, and established it more 
fully only in 1809, in his classic " Philosophie Zoologique." 2 
This admirable work is the first connected exposition of the 
Theory of Descent carried out strictly into all its conse- 
quences. By its purely mechanical method of viewing 
organic nature, and the strictly philosophical proofs brought 
forward in it, Lamarck's work is raised far above the pre- 
vailing dualistic views of his time ; and with the exception 
of Darwin's work, which appeared just half a century later, 
we know of none which we could in this respect place 
by the side of the " Philosophie Zoologique." How far it was 
in advance of its time is perhaps best seen from the cir- 


cumstance that it was not understood by most men, and for 
fifty years was not spoken of at all. Cuvier, Lamarck's 
greatest opponent, in his " Report on the Progress of Natural 
Sciences," in which the most unimportant anatomical inves- 
tigations are enumerated, does not devote a single word to 
this work, which forms an epoch in science. Goethe, also, who 
took such a lively interest in the French nature-philosophy 
and in " the thoughts of kindred minds beyond the Rhine,"' 
nowhere mentions Lamarck, and does not seem to have 
known the " Philosophie Zoologique " at all. The great repu- 
tation which Lamarck gained as a naturalist he does not owe 
to his highly important general work, but to numerous special 
treatises on the lower animals, particularly on Molluscs, 
as well as to an excellent " Natural History of Invertebrate 
Animals," which appeared, in seven volumes, between the 
years 1815-1822. The first volume of this celebrated work 
contains in the general introduction a detailed exposition of 
his theory of filiation. I can, perhaps, give no better 
idea of the extraordinary importance of the " Philosophie 
Zoologique" than by quoting verbatim some of the most 
important passages therefrom : — 

" The systematic divisions of classes, orders, families, 
genera, and species, as well as their designations, are the 
arbitrary and artificial productions of man. The kinds or 
species of organisms are of unequal age, developed one after 
the other, and show only a relative and temporary persist- 
ence ; species arise out of varieties. The differences in the 
conditions of life have a modifying influence on the organ- 
ization, the general form, and the parts of animals, and so 
has the use or disuse of organs. In the first beginning only 
the very simplest and lowest animals and plants came into 


existence ; those of a more complex organization only at a 
later period. The course of the earth's development, and 
that of its organic inhabitants, was continuous, not inter- 
rupted by violent revolutions. Life is purely a physical 
phenomenon. All the phenomena of life depend on 
mechanical, physical, and chemical causes, which are in- 
herent in the nature of matter itself. The simplest animals 
and the simplest plants, which stand at the lowest point in 
the scale of organization, have originated and still originate 
by spontaneous generation. All animate natural bodies or 
organisms are subject to the same laws as inanimate natural 
bodies or anorgana. The ideas and actions of the under- 
standing are the motional phenomena of the central nervous 
system. The will is in truth never free. Reason is only a 
higher degree of development and combination of judg- 

These are indeed astonishingly bold, grand, and far-reach- 
ing views, and were expressed by Lamarck sixty years ago ; 
in fact, at a time when their establishment, by a mass of 
facts, was not nearly as possible as it is in our day. Indeed 
Lamarck's work is really a complete and strictly monistic 
(mechanical) system of nature, and all the important general 
principles of monistic Biology are already enunciated by 
him : the unity of the active causes in organic and inorganic 
nature ; the ultimate explanation of these causes in the 
chemical and physical properties of matter itself; the 
absence of a special vital power, or of an organic final cause ; 
the derivation of all organisms from some few, most simple 
original forms, which have come into existence by spon- 
taneous generation out of inorganic matter ; the coherent 
course of the whole earth's history ; the absence of 

VOL. 1. I 


violent cataclysmic revolutions ; and in general the incon- 
ceivableness of any miracle, of any supernatural interference, 
in the natural course of the development of matter. 

The fact that Lamarck's wonderful intellectual feat met 
with scarcely any recognition, arises partly from the im- 
mense length of the gigantic stride with which he had 
advanced beyond the next fifty years, partly from its 
defective empirical foundation, and from the somewhat one- 
sided character of some of his arguments. Lamarck quite 
correctly recognizes Adaptation as the first mechanical 
cause which effects the continual transformation of organic 
forms, while he traces with equal justice the similarity 
in form of different species, genera, families, etc., to their 
blood-relationship, and thus explains it by Inheritance. 
Adaptation, according to him, consists in this, that the per- 
petual, slow change of the outer world causes a corre- 
sponding change in the actions of organisms, and thereby 
also causes a further change in their forms. He lays the 
greatest stress upon the effect of habit upon the use and 
disuse of organs. This is certainly of great importance 
in the transformation of organic forms, as we shall see 
later. However, the way in which Lamarck wished to 
explain exclusively, or at any rate mainly, the change of 
forms, is after all in most cases not possible. He says, for 
example, that the long neck of the giraffe has arisen from its 
constantly stretching out its neck at high trees, and from 
the endeavour to pick the leaves off their branches ; as 
giraffes generally inhabit dry districts, where only the 
foliage of trees afford them nourishment, they were forced 
to this action. In like manner the long tongues of wood- 
peckers, humming-birds, and ant-eaters, are said by him to 


have arisen from the habit of fetching their food out of 
narrow, small, and deep crevices or channels. The webs 
between the toes of the webbed feet in frogs and other 
aquatic animals have arisen solely from the constant endea- 
vour to swim, from striking their feet against the water, 
and from the very movements of swimming. Inheritance 
fixed these habits on the descendants, and finally, by further 
elaboration, the organs were entirely transformed. However 
correct, as a whole, this fundamental thought may be, yet 
Lamarck lays the stress too exclusively on habit (use and 
non-use of organs), certainly one of the most important, but 
not the only cause of the change of forms. Still this cannot 
prevent our acknowledging that Lamarck quite correctly 
appreciated the mutual co-operation of the two organic 
formative tendencies of Adaptation and Inheritance. What 
he failed to grasp is the exceedingly important principle of 
" Natural Selection in the Struggle for Existence," with 
which Darwin, fifty years later, made us acquainted. 

It still remains to be mentioned as a special merit of 
Lamarck, that he endeavoured to prove the development of 
the human race from other primitive, ape-like mammals. 
Here again it was, above all, to habit that he ascribed the 
transforming, the ennobling influence. He assumed that the 
lowest, original men had originated out of men-like apes, by 
the latter accustoming themselves to walk upright. The 
raising of the body, the constant effort to keep upright, in 
the first place led to a transformation of the limbs, to a 
stronger differentiation or separation of the fore and hinder 
extremities, which is justly considered one of the most 
essential distinctions between man and the ape. Behind, 
-the calf of the leg and the flat soles of the feet were 


developed ; in front, the arms and hands, for the purpose of 
seizing objects. The upright walk was then followed by a 
freer view over the surrounding objects, and led consequently 
to an important progress in mental development. Human 
apes thereby soon gained a great advantage over the other 
apes, and further, over surrounding organisms in general. 
In order to maintain the supremacy over them, they 
formed themselves into companies, and there arose, as in the 
case of all animals living in company, the desire of com- 
municating to one another then desires and thoughts. Thus 
arose the necessity of language, which, consisting at first of 
rough and disjointed sounds, soon became more connected, 
developed, and articulate. The development of articulate 
speech now in turn became the strongest lever for a further 
progressive development of the organism, and above all, of 
the brain, and so ape-like men became gradually and slowly 
transformed into real men. In this way the actual descent of 
the lowest and rudest primitive men from the most highly 
developed apes was distinctly maintained by Lamarck, and 
supported by a series of the most important proofs. 

The honour of being the chief French nature-philosopher is 
not usually assigned to Lamarck, but to Etienne Geoffroy St. 
Hilaire (the elder), born in 1771, the same in whom Goethe 
was especially interested, and with whom we have already 
become acquainted as Cuvier's most prominent opponent. 
He developed his ideas about the transformation of organic 
species as far back as the end of the last century> but 
published them only in the year 1828, and then in the fol- 
lowing years, especially in 1830, defended them bravely 
against Cuvier. Geoffroy St. Hilaire in all essentials 
adopted Lamarck's Theory of Descent, yet he believed that 



the transformation of animal and vegetable species was less 
effected by the action of the organism itself (by habit, 
practice, use, or disuse of organs) than by the "monde 
ambiant," that is, by the continual change of the outer 
world, especially of the atmosphere. He conceives the 
organism as passive, in regard to the vital conditions of the 
outer world, while Lamarck, on the contrary, regards it 
as active. Geoffroy thinks, for example, that birds origi- 
nated from lizard-like reptiles, simply by a diminution of 
the carbonic acid in the atmosphere, in consequence of which 
the breathing process became more animated and energetic 
through the increased proportion of oxygen in the atmosphere. 
Thus there arose a higher temperature of the blood, an 
increased activity of the nerves and muscles, and the scales 
of the reptiles became the feathers of the birds, etc. This 
conception is based upon a correct thought, but although 
the change of the atmosphere, as well as the change of every 
other external condition of existence, certainly effects 
directly or indirectly the transformation of the organism, 
yet this single cause is by itself too unimportant for such 
■effects to be ascribed to it. It is even less important than 
practice and habit, upon which Lamarck lays too much 
stress. Geoffroy's chief merit consists in his having vindi- 
cated the monistic conception of nature, the unity of 
organic forms, and the deep genealogical connection of the 
different organic types in the face of Cuvier's powerful 
influence. I have already mentioned in the preceding 
chapter (pp. 87, 88) the celebrated disputes between the two 
great opponents in the Academy of Paris, especially the 
fierce conflicts on the 22nd of February, and on the 19th of 
July, in which Goethe took so lively an interest. On that 


occasion Cuvier remained the acknowledged victor, and 
since that time very little, or rather nothing, more has been 
done in France to further the development of the Doctrine 
of Filiation, and complete the monistic theory of development. 
This is evidently to be ascribed principally to the repressive 
influence exercised by Cuvier's great authority. Even at 
the present day the majority of the French naturalists are 
the disciples and blind followers of Cuvier. In no civilized 
country of Europe has Darwin's doctrine had so little effect 
and been so little understood as in France, so that in the 
further course of our examination we need not take the 
French naturalists into consideration. At most, there are 
two distinguished botanists, among the recent French 
naturalists, whom we may mention as having ventured 
to express themselves in favour of the mutability and 
transformation of species. These two men are Naudin 
(1852) and Lecoq (1854). 

Having discussed the early services of German and 
French nature-philosophy in establishing the doctrine of 
descent, we turn to the third great country of Europe, to 
free England, which during the last ten years has become 
the chief seat and starting-point for the further working out 
and definite establishment of the theory of development. 
Englishmen, who now take such an active part in every 
great scientific progress of humanity, and are the first to 
promote the eternal truths of natural science, at the 
beginning of the century took but little part in the conti- 
nental nature-philosophy and its most important progress, 
the Theory of Descent. Almost the only earlier English 
naturalist whom we have here to mention is Erasmus 
Darwin, the grandfather of the reformer of the Theoiy of 


Descent. In 1795 he published, under the title of " Zoono- 
mia," a scientific work in which he expresses views very- 
similar to those of Goethe and Lamarck, without, however, 
then knowing anything about these two men. It is evident 
that the Theory of Descent at that time pervaded the intel- 
lectual atmosphere. Erasmus Darwin lays great stress upon 
the transformation of animal and vegetable species by their 
own vital action and by their becoming accustomed to 
changed conditions of existence, etc. Next, W. Herbert, in 
1822, expressed the opinion that species of animals and plants 
are nothing but varieties which have become permanent. 
In like manner Grant, in Edinburgh, in 1826, declared that 
new species proceed from existing species by continued 
transformation. In 1841 Freke maintained that all organic 
beings must be descended from a single primitive type. In 
1852 Herbert Spencer demonstrated minutely, and in a very 
clear and philosophic manner, the necessity of the Doctrine 
of Filiation, and established it more firmly in his excellent 
" Essays," which appeared in 1858, and in his " Principles of 
Biology," which was published at a later date. He has, at 
the same time, the great merit of having applied the theory 
of development to psychology, and of having shown that the 
emotional and intellectual faculties could only have been 
acquired by degrees and developed gradually. Lastly, we 
have to mention that in 1859 Huxley, the first of English 
zoologists, spoke of the Theory of Descent as the only 
hypothesis of creation reconcilable with scientific physiology. 
The same year produced the " Introduction to the Flora of 
Tasmania," in which Hooker, the celebrated English 
botanist, adopts the Theory of Descent, supporting it with 
important observations of his own. 


All the naturalists and philosophers with whom we have 
become acquainted in this brief historical survey, as men 
adopting the Theory of Development, merely arrived at the 
conception that all the different species of animals and 
plants which at any time have lived, and still live, upon 
the earth, are the gradually changed and transformed de- 
scendants of one or some few original and very simple 
prototypes, which latter arose out of inorganic matter by 
spontaneous generation. But none of them succeeded in 
placing this fundamental element of the doctrine of descent 
in relation with some cause, nor in satisfactorily explaining 
the transformation of organic species by the true demonstra- 
tion of its mechanical antecedents. Charles Darwin was 
the first who solved this most difficult problem, and this 
forms the broad gulf which separates him from his pre- 

The special merit of Charles Darwin is, in my opinion, 
twofold : in the first place, the doctrine of descent, the 
fundamental idea of which was already clearly expressed by 
Goethe and Lamarck, has been developed by him much 
more comprehensively, has been traced much more minutely 
in all directions, and carried out much more strictly and 
connectedly than by any of his predecessors ; and secondly, 
he has established a new theory, which reveals to us the 
natural causes of organic development, the acting causes 
(causse efficientes) of organic form-production, and of the 
changes and transformations of animal and vegetable species. 
This is the theory which we call the Theory of Selection, or 
more accurately, the Theory of Natural Selection (selectio 

When we reflect that (with the few exceptions above men- 


tioned) the whole science of Biology, before Darwin's time, 
was elaborated in accordance with the opposite views, and 
that almost all zoologists and botanists regarded the absolute 
independence of organic species as a self-evident inference 
from the results of all study of forms, we shall certainly not 
lightly value the twofold merit of Darwin. The false 
doctrine of the constancy and independent creation of 
individual species had gained such high authority, was so 
generally recognized, and was, moreover, so much favoured 
by delusive appearances, accepted by superficial observation, 
that, indeed, no small degree of courage, strength, and 
intelligence was required to rise as a reformer against its 
omnipotence, and to dash to pieces the structure artificially 
erected upon it. But, in addition to this, Darwin added to 
Lamarck's and Goethe's doctrine of descent the new and 
highly important principle of " natural selection." 

We must sharply distinguish the two points — though this 
is usually not done — first, Lamarck's Theory of Descent, 
which only asserts that all animal and vegetable species are 
■descended from common, most simple, and spontaneously 
generated prototypes; and secondly, Darwin's Theory of 
Selection, which shows us voliy this progressive transfor- 
mation of organic forms took place, and what causes, acting 
mechanically, effected the uninterrupted production of new 
forms, and the ever increasing variety of animals and 

Darwin's immortal merit cannot be justly estimated until 
a later period, when the Theory of Development, after over- 
throwing all other theories of creation, will be recognized as 
the supreme principle of explanation in Anthropology, and, 
consequently, in all other sciences. At present, while in 


the hot contest for truth the name of Darwin is the watch- 
word to the advocates of the natural theory of development, 
his merits are inaccurately appreciated on both sides, for 
some persons overestimate them as much as others under- 
estimate them. 

His merit is overestimated when he is regarded as the 
founder of the Theory of Descent, or of the whole of the 
Theory of Development. We have seen from the historical 
sketch in this and the preceding chapters, that the Theory of 
Development, as such, is not new; all philosophers who have 
refused to be led captive by the blind dogma of a super- 
natural creation, have been compelled to assume a natural 
development. But the Theory of Descent constituting the 
.specially biological part of the universal Theory of Develop- 
ment, had already been so clearly expressed by Lamarck, 
and carried out so fully by him to its most important con- 
sequences, that we must honour him as the real founder of 
it. Hence it is only the Theory of Selection, and not that 
of Descent, which may be called Darwinism ; but this is 
in itself of so much importance, that its value can scarcely 
be overestimated. 

Darwin's merit is naturally underestimated by all his 
opponents. But it is scarcely possible in this matter to 
point to scientific opponents, who are entitled by profound 
biological culture to pronounce an opinion. For among all 
the works opposed to Darwin and the Theory of Descent yet 
published, with the exception of that of Agassiz, not one 
deserves consideration, much less refutation ; all have so 
evidently been written either without thorough knowledge 
of biological facts, or without a clear philosophical under- 
standing of the question in hand. We need not trouble 


ourselves at all about the attacks of theologians and other un- 
scientific men, who really know nothing whatever of nature. 

The only eminent scientific adversary who still remains- 
opposed to Darwin and the whole theory of development is 
Louis Agassiz ; but the principle of his opposition in reality 
deserves notice only as a philosophical curiosity. In a 
French translation of his " Essay on Classification," 5 which 
we have spoken of before, published in Paris in 1869, 
Agassiz has most formally announced his opposition to 
Darwinism, which he had previously expressed in many 
ways. To this translation he has appended a treatise of 
sixteen pages, bearing the title, " Le Darwinisme. Classifi- 
cation de Haeckel." This curious chapter contains the most 
wonderful things ; as, for example, " Darwin's idea is a 
conception cl priori. Darwinism is a burlesque of facts- 
Science would renounce the claim which it has hitherto 
possessed to the confidence of earnest minds if such sketches 
were to be accepted as indications of a true progress." The 
following passage, however, is the climax of this strange 
polemic : " Darwinism shuts out almost the whole mass of 
acquired knowledge in order to retain and assimilate to 
itself that only which may serve its doctrine." 

Surely this is what we may call turning the whole affair 
topsy-turvy ! The biologist who knows the facts must be 
astounded at Agassiz's courage in uttering such sentences — 
sentences without a word of truth in them, and which he 
cannot himself believe ! The impregnable strength of the 
Theory of Descent lies just in the fact that all biological 
facts are explicable only through it, and that without it 
they remain unintelligible miracles. All our "laborious 
knowledge " in comparative anatomy and physiology — in 


embryology and palaeontology — in the doctrine of the 
geographical and topographical distribution of organisms, 
■etc., constitutes an irrefutable testimony to the truth of the 
Theory of Descent. 

In my General Morphology, especially in the sixth book 
(in the General Phylogeny), I have minutely refuted Agassiz's 
" Essay on Classification " in all essential points. The 
twenty-fourth chapter I have devoted to a very detailed and 
strictly scientific discussion of that section which Agassiz 
himself considers the most important (the groups or cate- 
gories of systematic zoology and botany), and have shown 
that this part of his work is purely chimerical, without any 
trace of real foundation. Agassiz takes good care not to 
venture anywhere to touch upon my refutation, because, 
forsooth, he is not in a position to produce anything 
substantial against it. He fights not with arguments, but 
with phrases. However, such opposition will not delay 
the complete victory of the Theory of Development, but 
only accelerate it. 

( "5 ) 



Charles Lyell's Principles of Geology. — His Natural History of the Earth's 
Development. — Origin of the Greatest Effects through the Multiplication 
of the Smallest Causes. — Unlimited Extent of Geological Periods. — ■ 
Lyell's Eefutation of Cuvier's History of Creation. — The Establishment 
of the Uninterrupted Connection of Historical Development by Lyell 
and Darwin. — Biographical Notice of Charles Darwin. — His Scientific 
Works. — His Theory of Coral Eeefs. — Development of the Theory of 
Selection. — A Letter of Darwin's. — The Contemporaneous Appearance 
of Darwin's and Alfred Wallace's Theory of Selection. — Darwin's Study 
of Domestic Animals and Cultivated Plants. — Andreas Wagner's notions 
as to the Special Creation of Cultivated Organisms for the good of 
Man. — The Tree of Knowledge in Paradise. — Comparison between Wild 
and Cultivated Organisms. — Darwin's Study of Domestic Pigeons. — 
Importance of Pigeon Breeding. — Common Descent of all Paces of 

During the thirty years, from 1830 until 1859, when 
Darwin's work appeared, the ideas of creation introduced 
by Cuvier remained predominant in the sciences of organic 
nature. People rested satisfied with the unscientific assump- 
tion, that in the course of the earth's history, a series of 
inexplicable revolutions had periodically annihilated the 
whole world of animals and plants, and that at the end of 
each revolution, and the beginning of a new period, a new, 


enlarged, and improved edition of the organic population had 
appeared. Although the number of these editions of creation 
was altogether problematical, and in truth could not be fixed 
■at all, and although the numerous advances which, during 
this time, were made in all the departments of zoology and 
botany demonstrated more and more that Cuvier's hypo- 
thesis was unfounded and untenable, and that Lamarck's 
natural theory of development was nearer the truth, yet the 
former maintained its authority almost universally among 
biologists. This must, above all, be ascribed to the venera- 
tion which Cuvier had acquired, and strikingly illustrates 
how injurious to the progress of humanity a faith in 
any definite authority may become. Authority, as Goethe 
once admirably said, perpetuates the individual, which 
as an individual should pass away, rejects and allows to 
pass that which should be held fast, and is the main 
obstacle to the advance of humanity. 

It is only by having regard to the great weight of Cuvier's 
authority, and to the mighty potency of human indolence, 
which is" with difficulty induced to depart from the broad 
and comfortable way of everyday conceptions, and to enter 
upon new paths not yet made easy, that we can comprehend 
how it is that Lamarck's Theory of Descent did not gain its 
due recognition until 1859, after Darwin had given it a new 
foundation. The soil had long been prepared for it by the 
works of Charles Lyell, another English naturalist, whose 
views are of great importance for the natural history of 
creation, and must accordingly here be briefly explained. 

In 1830 Charles Lyell published, under the title of 
" Principles of Geology," a work in which he thoroughly 
reformed the science of Geology and the history of the earth's 


development, and effected this reform in a manner similar to 
that in which, thirty years later, Darwin in his work reformed 
the science of Biology. Lyell's great treatise, which radically 
destroyed Cuvier's hypothesis of creation, appeared in the 
same year in which Cuvier celebrated his triumph over the 
nature-philosophy, and established his supremacy in the 
domain of morphology for the following thirty years. 
Whilst Cuvier, by his artificial hypothesis of creation and 
his theory of catastrophes connected with it, directly ob- 
structed the path of the theory of natural development, 
and cut off all chance of a natural explanation, Lyell once 
more opened a free road, and brought forward convincing 
geological evidence to show that Cuvier's dualistic concep- 
tions were as unfounded as they were superfluous. He 
demonstrated that those changes of the earth's surface, 
which are still taking place before our eyes, are perfectly 
sufficient to explain everything we know of the development 
of the earth's crust in general, and that it is superfluous and 
useless to seek for mysterious causes in inexplicable revolu- 
tions. He showed that we need only have recourse to the 
hypothesis of exceedingly long periods of time in order to 
explain the formation of the crust of the earth in the simplest 
and most natural manner by means of the very same causes 
which are still active. Many geologists had previously 
imagined that the highest chains of mountains which rise on 
the surface of the earth could owe their origin only to 
enormous revolutions transforming a great part of the earth's 
surface, especially to colossal volcanic eruptions. Such 
chains of mountains as those of the Alps or the Cordilleras 
were believed to have arisen direct from the fiery fluid of the 
interior of the earth, through an enormous chasm in the 


broken crust. Lyell, on the other hand, showed that we can 
explain the formation of such enormous chains of mountains 
quite naturally by the same slow and imperceptible risings and 
depressions of the earth's surface which are still continually 
taking place, and the causes of which are by no means 
miraculous. Although these depressions and risings may 
perhaps amount only to a few inches, or at most a few feet r 
in the course of a century; still, in the course of some 
millions of years they are perfectly sufficient to raise up the 
highest chains of mountains, without the aid of mysterious 
and incomprehensible revolutions. In like manner, the 
meteorological action of the atmosphere, the influence of rain 
and snow, and, lastly, the breakers on the coasts, which by 
themselves seem to produce an insignificant effect, must cause 
the greatest changes if we only allow sufficiently long 
periods for their action. The multiplication of the smallest 
causes produces the greatest effects. Drops of water produce 
a cavity in a rock. 

I shall afterwards be obliged again to recur to the im- 
measurable length of geological periods which are necessary 
for this purpose, for, as we shall see, Darwin's theory, as- 
well as that of Lyell, renders the assumption of immense 
periods absolutely necessary. If the earth and its organisms 
have actually developed in a natural way, this slow and 
gradual development must certainly have taken a length of 
time which surpasses our powers of comprehension. But as 
many men see in this very circumstance one of the principal 
difficulties in the way of those theories of development, I beg 
leave here to remark that we have not a single rational 
ground for conceiving the time requisite to be limited in any 
way. Not only many ordinary persons, but even eminent 


naturalists, make it their chief objection to these theories, 
that they arbitrarily claim too great a length of time : yet 
the ground of objection is scarcely intelligible. For it is 
absolutely impossible to see what can, in any way, limit us 
in assuming long periods of time. We have long known, 
even from the structure of the stratified crust of the earth 
alone, that its origin and the formation of neptunic rocks 
frorn water must have taken, at least, several millions of 
years. From a strictly philosophical point of view, it makes 
no difference whether we hypothetically assume for this pro- 
cess ten millions or ten thousand billions of years. Before 
us and behind us lies eternity. If the assumption of such 
enormous periods is opposed to the feelings of many, I regard 
this simply as the consequence of false notions which are 
impressed upon us from our 1 earliest youth concerning the 
short history of the earth, which is said to embrace only 
a few thousands of years. Albert Lange, in his " History 
of Materialism," 12 has convincingly shown that from a 
strictly philosophical point of view it is far less objec- 
tionable in a scientific hypothesis to assume periods which 
are too long than periods which are too short. Every 
process of development is the more intelligible the longer it 
is assumed to last. A short and limited period is the most 

I have no space here to enter minutely into Ly ell's great 
work, and will therefore mention only its most important 
result, which is, that he completely refuted Cuvier's history 
of creation with its mythical revolutions, and established in 
its place the constant and slow transformation of the earth's 
crust by the continued action of forces, which are still work- 
ing on the earth's surface, viz. the movement of water and 

vol. 1. K 


tlie volcanic fluid of the interior of earth. Lyell thus demon- 
strated a continuous and uninterrupted connection of the 
whole history of the earth, and he proved it so irrefutably, 
and established so convincingly the supremacy of the " ex- 
isting causes," that is, of the causes which are still active 
in the transformation of the earth's crust, that Geology in 
a short time completely renounced Cuvier's hypothesis. 

Now, it is remarkable that Palaeontology, the science of 
petrifactions, so far as it was pursued by botanists and zoolo- 
gists, remained apparently unaffected by this great progress 
in geology. Biology still continued to assume repeated new 
creations of the whole animal and vegetable kingdoms, at 
the beginning of every new period of the earth's history, 
although this hypothesis of individual creations, shoved into 
the world one after the other, without the assumption of 
Cuvier's cataclysms, became pure nonsense, and lost its 
foundation. It is evidently perfectly absurd to assume a 
distinct new creation of the whole world of animals and 
plants at definite epochs, without the crust of the earth 
itself experiencing any considerable general revolution. 
And although this conception is most closely connected 
with Cuvier's theory of catastrophes, still it prevailed when 
the latter had been completely destroyed and abandoned. 

It was reserved for the great English naturalist, Charles 
Darwin, to remove this contradiction, and to show that the 
organic beings of the earth have a history as continuous and 
connected as the inorganic crust of the earth ; that animals 
and plants have arisen from one another by as gradual a 
transmutation as that by which the varying forms of the 
earth's crust, the forms of the continents, and of the seas 
surrounding and separating them, have arisen out of earlier 


•and quite different forms. In this respect we may truly say 
that in the domain of Zoology and Botany Darwin made 
the same progress as Lyell, his great countryman, in the 
domain of Geology. Both proved the uninterrupted con- 
nection of the historical development, and demonstrated a 
gradual transmutation of the different conditions succeeding 
one another. 

The special merit of Darwin, as I have already remarked 
in a preceding chapter, is twofold. In the first place, he has 
treated the Theory of Descent, put forth by Lamarck and 
Goethe, in a much more comprehensive manner, as a whole, 
and carried it out in a much more connected manner, than 
had been done by any one of his predecessors. Secondly, 
he has established the causal foundation of this Theory of 
Descent by the Theory of Selection, which is peculiarly his 
own ; that is, he has demonstrated the acting causes of the 
changes which the Theory of Descent simply stated, as facts. 
The Theory of Descent, introduced into Biology in 1809, by 
Lamarck, asserts that all the different species of animals 
and plants are descended from a single or some few most 
simple prototypes, produced by spontaneous generation. 
The Theory of Selection, established in 1859 by Darwin, 
shows us why this must be so ; it points out the acting- 
causes in a manner with which Kant would have been 
■delighted, and indeed, in the domain of organic nature, 
Darwin has become the Newton whose advent Kant 
thought himself entitled prophetically to deny. 

Now, before we approach Darwin's theory, it will perhaps 
be of interest to notice a few details as to the personal 
character of this great naturalist, as to his life, and the 
way in which he was led to form his doctrine. Charles 


Robert Darwin was born at Shrewsbury, on the Severn, 
on the 12th of February, 1809; therefore, at present he is 
sixty-three years old. In his seventeenth year (1825) he 
entered the University of Edinburgh, and two years later 
Christ's College, Cambridge. When scarcely twenty-two^ 
years old, in 1831, he was invited to take part in a 
scientific expedition which was sent out by England, 
in order to survey accurately the southernmost point of 
South America, and to examine several parts of the 
South Seas. This expedition, like many other voyages of 
inquiry fitted out in a praiseworthy manner by England, 
had scientific objects, and at the same time was intended 
to solve practical problems relating to navigation. The 
vessel, commanded by Captain Fitzroy, appropriately bore 
the symbolic name of the Beagle. The voyage of the 
Beagle, which lasted five years, was of the highest im- 
portance to the full development of Darwin's genius ; for 
in the veiy first year, when he set his foot on the soil 
of South America, the outline of the doctrine of descent 
dawned upon him. Darwin himself .has described this 
voyage in a work which is written in a very attractive 
style, and the perusal of which I strongly recommend to 
the reader. This book of travel, which lies far above the 
usual average in interest, not only shows in a very charming 
manner Darwin's amiable character, but we can in many 
ways recognize the various steps by which he arrived at his 
conceptions. The result of the voyage was, first, a large 
scientific work, the zoological and geological portion of 
which belong in a great measure to Darwin ; and secondly, 
a celebrated work by him alone on Coral Reefs, which in 
itself would have sufficed to secure to him a lasting reputa- 


tion. It is well known that the islands in the South Seas 
consist for the most part of coral reefs, and are surrounded 
by them. Formerly no satisfactory explanation could be 
given of their different and remarkable forms, and of their 
relation to those islands which are not formed of corals. 
It was reserved for Darwin to solve this difficult problem, 
for together with the constructive action of the coral 
zoophytes, he assumed geological risings and depressions 
of the bottom of the sea to account for the origin of 
the different forms of reefs. Darwin's Theory of the 
Origin of Coral Reefs, like his later one as to the Origin of 
Organic Species, is a theory which fully explains the 
phenomenon, and for this purpose assumes only the simplest 
natural causes, without hypothetically supporting it with 
any unknown processes. Among the remaining works of 
Darwin, I must not pass over his excellent monograph on 
Cirrhipedia, a curious class of marine animals, which in 
their outward appearance resemble mussels, and were 
actually considered by Cuvier as Molluscs possessing two 
shells, while in truth they belonged to the Crustacea (crabs). 
The extraordinary hardships to which Darwin had been 
exposed during his voyage in the Beagle had injured his 
health to such a degree, that after his return home he was 
obliged to withdraw from the restless turmoil of London life, 
and since then has lived in quiet retirement on his estate at 
Down, near Bromley, in Kent. This seclusion from the rest- 
less activity of the great city certainly exercised a beneficial 
influence upon Darwin, and it is probable that we owe to it, 
at least partially, the formation of the Theory of Selection. 
Undisturbed by the various engagements which in London 
would have wasted his strength, he was enabled to concen- 


trate his attention upon the great problem to which his 
mind had been turned during his voyage in the Beagle. In 
order to show what kind of observations during the voyage 
principally gave rise to the fundamental idea of the Theory 
of Selection, and in what manner he afterwards worked 
it out, I shall insert here a passage from a letter which he 
addressed to me on the 8th of October, 1864. 

Letter from Charles, Barvnnto Haechel, 8th October, 1864 

" In South America three classes of facts were brought 
strongly before my mind. Firstly, the manner in which 
closely allied species replace species in going southward. 
Secondly, the close affinity of the species inhabiting the 
islands near South America to those proper to the con- 
tinent. This struck me profoundly, especially the differ- 
ence of the species in the adjoining islets in the Galopago& 
Archipelago. Thirdly, the relation of the living Edentata 
and Rodentia to the extinct species. I shall never forget 
my astonishment when I dug out a gigantic piece of armour 
like that of the living armadillo. 

" Reflecting on these facts, and collecting analogous ones, it 
seemed to me probable that allied species were descended 
from a common parent. But for some years I could not 
conceive how each form became so excellently adapted to 
its habits of life. I then began systematically to study 
domestic productions, and after a time saw clearly that 
man's selective power was the most important agent. I was 
prepared, from having studied the habits of animals, to ap- 
preciate the struggle for existence, and my work in geology 
gave me some idea of the lapse of past time. Therefore, 
when I happened to read " Malthus on Population," the idea 

darwin's method of study. 135 

of natural selection flashed on me. Of all the minor points, 
the last which I appreciated was the importance and cause 
of the principle of divergence." 

During the leisure and retirement in which Darwin lived 
after his return, he occupied himself, as we see from this 
letter, first and specially with the study of organisms in 
their cultivated state ; that is, domestic animals and garden 
plants. This was undoubtedly the most likely way to 
arrive at the Theory of Selection. In this, as in all his 
laboms, Darwin proceeded with extreme care and accuracy. 
With wonderful caution and self-denial, he published nothing 
on this subject during a period of twenty-one years, from 1837 
to 1858, not even a preliminary sketch of his theory, which 
he had written as early as 1844. He was always anxious to 
collect stiU more certain experimental proofs, in order to be 
able to establish his theory in a complete form, and on the 
broadest possible foundation of experience. While he was 
thus aiming at the greatest possible perfection, which might 
perhaps have led him never to publish his theory at all, he 
was fortunately disturbed by a countryman of his, who, 
independently of Darwin, had discovered the Theory of 
Selection, and in 1858 sent its outlines to Darwin himself, 
with the request to hand them to Lyell for publication in 
some English journal. This was Alfred Wallace, one of the 
boldest and most distinguished scientific travellers of modern 
times. For many years Wallace had wandered alone in the 
wilds of the Sunda Islands, in the dense primitive forests of 
the Indian Archipelago ; and during this close and compre- 
hensive study of one of the richest and most interesting 
parts of the earth, with its great variety of animals and 


plants, lie had arrived at exactly the same general views 
regarding the origin of organic species as Darwin. Lyell 
and Hooker, both of whom had long known Darwin's 
work, now induced him to publish a short extract from his 
manuscripts simultaneously with the manuscript sent him 
by Wallace. They appeared in the Journal of the Linnean 
Society, August, 1858. 

Darwin's great work "On the Origin of Species," in 
which the Theory of Selection is carried out in detail, ap- 
peared in November, 1859. Darwin himself, however, 
characterizes this book (of which a fifth edition appeared 
in 1869, and the German translation by Bronn as early as 
I860) 1 as only a preliminary extract from a larger and 
more detailed work, which is to contain a mass of facts in 
favour of his theory, and comprehensive and experimental 
proofs. The first part of the larger work promised by 
Darwin appeared in 1868, under the title, " The Variations 
of Animals and Plants in the State of Domestication," and 
has been translated into German by Victor Carus. 14 It con- 
tains a rich abundance of the most valuable evidence as 
to the extraordinary changes of organic forms which man 
can produce by cultivation and artificial selection. How- 
ever much we are indebted to Darwin for this abundance of 
convincing facts, still we do not by any means share the 
opinion of those naturalists who hold that the Theory of 
Selection requires for its actual proof these further details. 
It is our opinion that Darwin's first work, which appeared 
in 1859, already contains sufficient proof. The unassailable 
strength of his theory does not lie in the immense amount 
of individual facts that may be adduced as proofs, but in 
the harmonious connection of all the great and general phe- 


nomena of organic nature, which agree in bearing testimony 
to the truth of the Theory of Selection. 

Darwin, at first, intentionally did not notice the important 
conclusion from his Theory of Descent, namely, the descent 
of the human race from other mammals. It was not till 
this highly important conclusion had been definitely estab- 
lished by other naturalists as the necessary sequel of the 
doctrine of descent, that Darwin himself expressly endorsed 
it, and thereby completed his system. This was done in 
the highly interesting work, "The Descent of Man, and 
Sexual Selection," which appeared as late as 1871, and has 
likewise been translated into German by Victor Cams. 48 

The careful study which Darwin devoted to domestic 
animals and cultivated plants was of the greatest import- 
ance in establishing the Theory of Selection. The infinitely 
varied changes of form which man has produced in these 
domesticated organisms by artificial selection are of the 
very highest importance for a right understanding of animal 
and vegetable forms ; and yet this study has, down to the 
most recent times, been most grossly neglected by zoologists 
and botanists. Without entering upon the discussion of the 
significance to be attached to the idea of species itself, they 
have filled not only bulky volumes, but whole libraries, 
with descriptions of individual species, and with most 
childish controversies as to whether these species are good, 
•or tolerably good, and bad, or tolerably bad. If naturalists 
instead of spending their time on these useless fancies had 
duly studied cultivated organisms, and had examined the 
transmutation of the living forms, instead of the individual 
dead ones, they would not have been led captive so long by 
the fetters of Cuvier's dogma. But as cultivated organisms 


are so extremely inconvenient to the dogmatic conception 
of the permanence of species, naturalists to a great extent 
intentionally did not concern themselves about them, and 
even celebrated naturalists have often expressed the opinion 
that cultivated organisms, domesticated animals and garden 
plants, are artificial productions of man, and that their 
formation and transformation could not decide anything 
about the nature of species and about the origin of the 
forms of species that live in a natural state. 

This perverse view went so far that, for example, Andreas 
Wagner, a zoologist of Munich, quite seriously made the 
following ridiculous assertion: — "Animals and plants in 
their wild state have been called into being by the Creator 
as distinctly different and unchangeable species ; but in the 
case of domestic animals and cultivated plants this was not 
necessary, because he formed them from the beginning for the 
use of man. The Creator formed man out of a clod of earth,, 
breathed the living breath into his nostrils, and then created 
for him the different useful domestic animals and garden 
plants, among which he thought well to save himself the 
trouble of distinguishing species." Unfortunately, Andreas 
Wagner does not tell us whether the Tree of Knowledge 
in Paradise was a " good " wild species, or, as a cultivated 
plant, " no species " at all. As the Tree of Knowledge was 
placed by the Creator in the centre of Paradise, we might 
be inclined to believe that it was a highly favoured culti- 
vated plant, and therefore no species at all. But since, on 
the other hand, the fruit of the Tree of Knowledge was 
forbidden to man, and since many men, as Wagner himself 
clearly shows, have never eaten of the fruit, it was 
evidently not created for the use of man, and therefore in 


all probability was a real species! What a pity Wagner 
has not given us any information about this important 
and difficult problem ! 

Now, however ridiculous this view may appear to us, it 
is only the logical sequence of a false view (which is widely 
spread) of the special nature of cultivated organisms, and 
one may occasionally hear similar objections from naturalists 
of great reputation. I must most decidedly, and at ouce,. 
condemn this utterly false conception. It is the same per- 
verseness which is committed by physicians who maintain 
that diseases are artificial productions, and not natural 
phenomena. It has been a work of hard labour to combat 
this prejudice, and it is only in recent times that men have 
generally adopted the view that diseases are nothing 
but natural changes of the organisms, or really natural 
phenomena of life, which are produced by changed and 
abnormal conditions of existence. Disease, therefore, is not 
a life beyond Nature's realm (vita prseter naturam), as the 
early physicians used to say, but a natural life under con- 
ditions which produce illness and threaten the body with 
danger. Just in the same manner, cultivated organic forms 
are not artificial works of man, but natural productions 
which have arisen under the influence of peculiar conditions 
of life. Man by his culture can never directly produce a 
new organic form, but he can breed organisms under new 
conditions of life, which are such as to influence and trans^ 
form them. All domestic animals and all garden plants 
are originally descended from wild species, which have been 
transformed by the peculiar conditions of culture. 

A thorough comparison of cultivated forms (races and 
varieties) with organisms not altered by cultivation (species- 


and varieties), is of the utmost importance to the theory of 
selection. What is most surprising in such a comparison is 
the remarkably short time in which man can produce a 
new form, and the high degree in which this form, pro- 
duced by man, can deviate from the original form. While 
wild animals and plants, one year after another, appear 
to the zoologist and botanist approximately in the same 
form, so as to have given rise to the false doctrine of the 
constancy of species, domestic animals and garden plants, 
, on the other hand, display the greatest changes within a 
few years. The perfection which gardeners and farmers 
have attained in the art of selection now enables them, in 
the space of a few years, arbitrarily to create entirely new 
animal and vegetable forms. For this purpose it is only 
necessary to keep and propagate the organism under the 
influence of special conditions — which are capable of pro- 
ducing new formations —and even at the end of a few 
generations new species may be obtained, which differ from 
the original form in a much higher degree than so-called 
good species in a wild state differ from one another. This 
fact is extremely important, and we cannot lay sufficient 
stress upon it. The assertion is not true that cultivated 
forms descended from one and the same primary form do 
not differ from one another as much as wild animal and 
vegetable species differ among themselves. If we only make 
comparisons, without prejudice, we can very easily perceive 
that a number of races or varieties which have been derived 
from a single cultivated form, within a short series of years, 
differ from one another in a higher degree than so-called 
good species (bonse species), or even different genera of one 
family, in the wild state. 


In order to establish this extremely important fact as- 
firmly as possible by experiments, Darwin decided to make 
a special study of the whole extent of variation in form in 
a single group of domesticated animals, and for this purpose 
he chose the domestic pigeons, which are in many respects- 
especially suited for such a study. For a long time he kept 
on his estate all possible races and varieties of pigeons 
Avhich he was able to procure, and he was helped in this by 
rich contributions from all parts of the world. He also 
joined two London pigeon clubs, the members of which pas- 
sionately, and with truly artistic skill, carry on the breeding 
of the different forms of pigeons. Lastly, he formed con- 
nections with some of the most celebrated pigeon-fanciers - r 
so that he could command the richest experimental material. 

The art of, and fancy for, pigeon breeding is very ancient. 
Even more than 3,000 years before Christ, it was carried on 
by the Egyptians. The Romans, under the emperors, laid 
out enormous sums upon the breeding of pigeons, and kept 
accurate pedigrees of their descent, just as the Arabs keep 
genealogical pedigrees of their horses, and the Mecklenburg 
aristocracy of their own ancestors. In Asia, too, among 
the wealthy princes, pigeon breeding was a very ancient 
fancy ; in 1600, the court of Akber Khan possessed more 
than 20,000 pigeons. Thus in the course of several centuries, 
and in consequence of the various methods of breeding 
practised in the different parts of the world, there has 
arisen out of one single originally tamed form, an immense 
number of different races and varieties, which in their most 
divergent forms are extremely different from one another, 
and are often curiously characterized. 

One of the most striking races of pigeons is the well- 


known, fan-tailed pigeon, which spreads its tail like the pea- 
cock, and carries a number of (from thirty to forty) feathers 
placed in the form of radii, while other pigeons possess 
much fewer tail feathers — generaUy twelve. We may here 
mention that the number of feathers on the tails of birds is 
considered by naturalists of great value as a systematic dis- 
tinction, so that whole orders can thereby be distinguished. 
For example, singing birds, almost without exception, possess 
twelve tail feathers; chirping birds (Strisores) ten, etc. 
Several races of pigeons, moreover, are characterized by a 
tuft of neck feathers, which form a kind of periwig ; others 
by grotesque transformation of their beaks and feet, by pecu- 
liar and often very remarkable decorations, as, for example, 
skinny lappets, which develop on the head ; by a large 
crop, which is formed by the gullet being strongly inclined 
forward, etc. Remarkable, also, are the strange habits which 
many pigeons have acquired ; for example, the turtle pigeons 
and the trumpeters with their musical accomplishments, the 
carriers with their topographical instinct. The tumblers 
have the strange habit of ascending into the air in great 
numbers, then turning over and falling down through the 
air as if dead. The ways and habits of these endless races 
of pigeons — the form, size, and colour of the individual parts 
of their bodies, and their proportions, differ in a most 
astonishing degree from one another ; in a much higher de- 
gree than is the case with the so-called good species, or even 
with the perfectly distinct genera, of wild pigeons. And 
what is of the greatest importance, is the fact that these 
differences are not confined to the external form, but extend 
even to the most important internal parts ; there even occur 
great modifications of the skeleton and of the muscular 


tissues. For example, we find great differences in the 
number of vertebrae and ribs, in the size and shape of the 
gaps in the breast-bones, in the size and shape of the merry- 
thought, in the lower jaw, in the facial bones, etc. In short, 
the bony skeleton, which morphologists consider a very 
permanent part of the body, and which never varies to such 
an extent as the external parts — shows such great changes, 
that many races of pigeons might be described as special 
genera, and this would doubtless be done if all these different 
forms had been found in a wild and natural state. 

How far the differences of the races of pigeons have been 
carried is best shown by the fact that all pigeon breeders 
are unanimously of opinion that each peculiar or specially 
marked race of pigeons must be derived from a correspond- 
ing wild original species. It is true every one assumes a 
different number of original species. Yet Darwin has most 
convincingly and acutely proved that all these pigeons, 
without exception, must be derived from a single wild 
primary species — from the blue rock-pigeon (Columba livia.) 
In like manner, it can be proved of- most of the domestic 
animals and cultivated plants, that all the different races 
are descendants of a single original wild species which has 
been brought by man into a cultivated condition. 

An example similar to that of the domestic pigeons is fur- 
nished among mammals by our tame rabbit. All zoologists, 
without exception, have long considered it proved that all 
its races and varieties are descended from the common wild 
rabbit, that is, from a single primary species. And yet the 
extreme foi-ms of these races differ to such a degree from 
one another, that every zoologist, if he met with them in a 
wild state, would unhesitatingly designate them not only as 


an entirely distinct "good species/' but even as species of 
entirely different genera of the Leporid family. Not only 
does the colour, length of hair, and other qualities of the fur 
of the different tame races of rabbits vary exceedingly, and 
form extremely broad contrasts, but, what is still more im- 
portant, the typical form of the skeleton and its individual 
parts do so also, especially the form of the skull and the 
jaw (which is of such importance in systematic arrange- 
ment) ; further, the relative proportion of the length of the 
ears, legs, etc. In all these respects the races of tame rabbits 
avowedly differ from one another far more than all the dif- 
ferent forms of wild rabbits and hares which are scattered 
over all the earth, and are the recognized " good species " of 
the genus Lepus. And yet, in the face of these clear facts, the 
opponents of the theory of development maintain that the 
wild species are not descended from a common prototype, 
although they at once admit it in the case of the tame 
races. With opponents who so intentionally close their 
eyes against the clear light of truth, no further dispute can 
be carried on. 

While in this manner it appears certain that the domestic 
races of pigeons, of tame rabbits, of horses, etc., notwith- 
standing the remarkable difference of their varieties, are 
descended in each case from but one wild, so-called 
" species " ; yet, on the other hand, it is certainly probable 
that the great variety of races of some of the domestic ani- 
mals, especially dogs, pigs, and oxen, must be ascribed to 
the existence of several wild prototypes, which have become 
mixed. It is, however, to be observed that the number of 
these originally wild primary species is always much 
smaller than that of the cultivated forms proceeding from 


their mingling and selection, and naturally they were 
originally derived from a single primary ancestor, com- 
mon to the whole genus. In no case is each separate 
cultivated race descended from a distinct wild species. 

In opposition to this, almost all farmers and gardeners 
maintain, with the greatest confidence, that each separate race 
bred by them must he descended from a separate wild 
primary species, because they clearly perceive the differences 
of the races, and attach very high importance to the inherit- 
ance of their qualities ; but they do not take into consider- 
ation the fact that these qualities have arisen only by the 
slow accumulation of small and scarcely observable changes. 
In this respect it is extremely instructive to compare culti- 
vated races with wild species. 

Many naturalists, and especially the opponents of the 
Theory of Development, have taken the greatest trouble to 
discover some morphological or physiological mark, some 
characteristic property, whereby the artificially bred and 
cultivated races may be clearly and thoroughly distin- 
guished from wild species which have arisen naturally. 
All these attempts have completely failed, and have led 
only with increasing certainty to the result, that such a 
distinction is altogether impossible. I have minutely dis- 
cussed this fact, and illustrated it by examples in my criti- 
cism of the idea of species. (Gen. Morph. ii. 323-364.) 

I may here briefly touch on yet another side of this 
question, because not only the opponents, but even a few of 
the most distinguished followers of Darwin — for example, 
Huxley — have regarded the phenomena of bastard-breeding, 
or hybridism, as one of the weakest points of Darwinism. 
Between cultivated races and wild species, they say, there 

vol. 1. l 


exists this difference, that the former are capable of pro- 
ducing fruitful bastards, but that the latter are not. Two 
different cultivated races, or wild varieties of one species, 
are said in all cases to possess the power of producing 
bastards which can fruitfully mix with one another, or 
with one of their parent forms, and thus propagate them- 
selves ; on the other hand, two really different species, two 
cultivated or wild species of one genus, are said never to be 
able to produce from one another bastards which can be 
fruitfully crossed with one another, or with one of their 
parent species. 

As regards the first of these assertions, it is simply re- 
futed by the fact that there are organisms which do not 
mix at all with their own ancestors, and therefore can 
produce no fruitful descendants. Thus, for example, our 
cultivated guinea-pig does not bear with its wild Brazilian 
ancestor ; and again, the domestic cat of Paraguay, which is 
descended from our European domestic cat, no longer bears 
with the latter. Between different races of our domestic 
dogs, for example, between the large Newfoundland dogs 
and the dwarfed lap-dogs, breeding is impossible, even for 
simple mechanical reasons. A particularly interesting in- 
stance is afforded by the Porto-Santo rabbit (Lepus Hux- 
leyi). In the year 1419, a few rabbits, born on board 
ship of a tame Spanish rabbit, were put on the island of 
Porto Santo, near Madeira. These little animals, there 
being no beasts of prey, in a short time increased so enor- 
mously that they became a pest to the country, and even 
compelled a colony to remove from the island. They still 
inhabit the island in great numbers; but in the course of 
four hundred and fifty years they have developed into a quite 


peculiar variety — or if you will have t it, into a "good 
species " — which is distinguished by a peculiar colour, a rat- 
like shape, small size, nocturnal life, and extraordinary wild- 
ness. The most important fact, however, is that this new 
species, which I call Lepus Huxleyi, no longer pairs with its 
European parent rabbit, and no longer produces bastards 
with it. 

On the other hand, we now know of numerous examples 
■of fruitful genuine bastards ; that is, of mixings that have 
proceeded from the crossing of two entirely different species, 
and yet propagate themselves with one another as well as 
with one of their parent species. A number of such bastard 
species (species Hybrids) have long been known to botanists ; 
for example, among the genera of the thistle (Cirsium), the 
laburnum (Cytisus), the bramble (Rubus), etc. Among 
animals also they are by no means rare, perhaps even very 
frequent. We know of fruitful bastards which have arisen 
from the crossing of two different species of a genus, as 
among several genera of butterflies (Zygasna, Saturnia), the 
family of carps, finches, poultry, dogs, cats, etc. One of the 
most interesting is the hare-rabbit (Lepus Darwinii), the 
bastard of our indigenous hare and rabbit, many genera- 
tions of which have been bred in France, since 1850, for 
gastronomic purposes. I myself possess such hybrids, the 
products of pure in-breeding, that is, both parents of which 
are themselves hybrids by a hare-father and a rabbit-mother. 
I possess them through the kindness of Professor Conrad, 
who has repeatedly made these experiments in breeding on 
his estate. The half-blood hybrid thus bred, which I name 
in honour of Darwin, appears to propagate itself through 
many generations by pure in-breeding, just as well as any 


genuine species. Although on the whole it is more like its 
mother (rabbit), still in the formation of the ears and of the 
hind-legs, it possesses distinct qualities of its father (hare). 
Its flesh has an excellent taste, rather resembling that of a 
hare, though the colour is more like that of a rabbit. But 
the hare (Lepus timidus) and the rabbit (Lepus cuniculus) 
are two species of the genus Lepus, so different that no> 
systematic zoologist will recognize them as varieties of one 
species. Both species, moreover, live in such different ways, 
and in their wild state entertain so great an aversion 
towards one another, that they do not pair so long as they 
are left free. If, however, the newly-born young ones of 
both species are brought up together, this aversion is not 
developed; they pair with one another and produce the 
Lepus Darwinii. 

Another remarkable instance of the crossing of different 
species (where the two species belong even to different 
genera !) is furnished by the fruitful hybrids of sheep and 
goats which have for a long time been bred in Chili for in- 
dustrial purposes. On what unessential circumstances in 
the sexual mingling the fertility of the different species 
depend, is shown by the fact that he-goats and sheep in 
their mingling produce fruitful hybrids, while the ram and 
she-goat pair very rarely, and then without result. The 
phenomena of hybridism to which undue importance has 
been erroneously attributed are thus utterly unmeaning, so 
far as the idea of species is concerned. The breeding of 
hybrids does not enable us, any more than other phenomena, 
thoroughly to distinguish cultivated races from wild species ; 
and this circumstance is of the greatest importance in the 
Theory of Selection. 

( 149 ) 



Darwinism (Theory of Selection) and Lamarckism (Theory of Descent). — 
The Process of Artificial Breeding. — Selection of the Different Indivi- 
duals for After-breeding. — The Active Causes of Transmutation. — Change 
connected with Pood, and Transmission by Inheritance connected with 
Propagation. — Mechanical Nature of these Two Physiological Functions. 
— The Process of Natural Breeding : Selection in the Struggle for 
Existence.— Malthus' Theory of Population. — The Proportion between 
the Numbers of Potential and Actual Individuals of every Species of 
Organisms. — General Struggle for Existence, or Competition to attain 
the Necessaries of Life.— Transforming Force of the Struggle for 
Existence. — Comparison of Natural and Artificial Breeding — Selection 
in the Life of Man. — Military and Medical Selection. 

It is, properly speaking, not quite correctly that the Theory 
•of Development, with which we are occupied in these pages, 
is usually called Darwinism. For, as we have seen from 
the historical sketch in the previous chapters, the most 
important foundation of the Theory of Development — that 
is, the Doctrine of Filiation, or Descent — had already been 
distinctly enunciated at the beginning of our century, and 
had been definitely introduced into science by Lamarck. 
The portion of the Theory of Development which maintains 
the common descent of all species of animals and plants from 
the simplest common original forms might, therefore, in 


honour of its eminent founder, and with full justice, he called 
Lamarckism, if the merit of having earned out such a 
principle is to he linked to the name of a single distinguished 
naturalist. On the other hand, the Theory of Selection, or 
breeding, might be justly called Darwinism, being that por- 
tion of the Theory of Development which shows us in what 
way and why the different species of organisms have de- 
veloped from those simplest primary forms. (Gen. Morph. ii. 

It is true we find the first trace of an idea of natural 
selection even forty years before the appearance of Darwin's 
work. For in the year 1818 there was published a paper "On 
a woman of the white race whose skin partly resembled that 
of a negro," which had been read before the Royal Society 
as early as 1813. Its author, Dr. W. C. Wells, states that 
negroes and mulattoes are distinguished from the white race 
by their immunity from certain tropical diseases. On this 
occasion he remarks that all animals have a tendency to 
change up to a certain degree, and that farmers, by availing 
themselves of this tendency, and also by selection, improve 
their domestic animals ; and then he adds, that what is done 
in this latter case "by art, seems to be done with equal 
efficiency, though more slowly, by nature, in the formation 
of varieties of mankind fitted for the country which they 
inhabit. Of the accidental varieties of man which wovdd 
occur among the first few and scattered inhabitants of the 
middle regions of Africa, some one would be better fitted than 
the others to bear the diseases of the country. This race 
would consequently multiply, while the others would de- 
crease ; not only from then inability to sustain the attacks 
of disease, but from their incapacity of contending with 


their more vigorous neighbours. The colour of this vigorous 
race I take for granted, from what has been already said, 
would he dark. But the same disposition to form varieties 
still existing, a darker and a darker race would in the course 
of time occur ; and as the darkest would be the best fitted 
for the climate, this would at length become the most pre- 
valent, if not the only race, in the particular country in 
which it had originated." He then extends these same 
views to the white inhabitants of colder climates. Although 
Wells clearly expresses and recognizes the principle of 
natural selection, yet it is applied by him only to the very 
limited problem of the origin of human races, and not at 
all to that of the origin of animal and vegetable species. 
Darwin's great merit in having independently developed 
the Theory of Selection, and having brought it to complete 
and well merited recognition, is as little affected by the 
earlier and long forgotten remark of Wells, as by some other 
fragmentary observations about natural selection made by 
Patrick Mathew, and hidden in his book on "Timber for 
Shipbuilding, and the Cultivation of Trees," which appeared 
in 1831. The celebrated traveller, Alfred Wallace, who 
developed the Theory of Selection independently of Darwin, 
and had published it in 1858, simultaneously with Darwin's 
first contribution, likewise stands far behind his greater and 
elder countryman in regard to profound conception, as 
well as to extended application of the theory. In fact Dar- 
win, by his extremely comprehensive and ingenious develop- 
ment of the whole doctrine, has acquired a fair claim to see 
the theory connected with his own name. 

This Theory of Selection, Darwinism in its proper sense, 
to the consideration of which we now turn our attention, 


rests essentially (as has already been intimated in tlie last 
chapter) upon the comparison of those means which man 
employs in the breeding of domestic animals and the culti- 
vation of garden plants, -with those processes which in 
free nature, outside the cultivated state, lead to the coming 
into existence of new species and new genera. We must 
therefore, in order to understand the latter processes, 
first turn to the artificial breeding by man, as was, in fact, 
done by Darwin himself. We must inquire into the results 
to which man attains by his artificial breeding, and what 
means are applied in order to obtain those results ; and we 
must then ask ourselves, " Are there in nature similar forces 
and causes acting similarly to those resorted to by man ? " 

First, in regard to artificial breeding, we start from the 
fact last discussed above, viz. that its products in some 
cases differ from one another much more than the produc- 
tions of natural breeding. It is a fact that races or varieties 
often differ from one another in a much greater degree and 
in much more important qualities than many so-called 
species, or " good species," — nay, sometimes even more than 
so-called "good genera" in their natural state. Compare, 
for example, the different kinds of apples which the art 
of horticulture has derived from one and the same 
original apple-form, or compare the different races of horses 
which their breeders have derived from one and the same 
original form of horse, and it will be easily observed that 
the differences of the most different forms are extremely 
important, and much more important than the so-called 
" specific differences," which are referred to by zoologists and 
botanists when comparing wild forms for the purpose of 
distinguishing several so-called " good species." 


Now, by what means does man produce this extraordinary 
difference or divergence of several forms which are proved 
to be descended from the same primary form ? In order to 
answer this question, let us follow a gardener who desires 
to produce a new form of a plant, which is distinguished by 
the beautiful colour of its flowers. He will first of all make 
a selection from a great number of plants which are seed- 
lings from one and the same parent. He will pick out 
those plants which exhibit most distinctly the colour of 
flower he desires. The colour of flowers is a very change- 
able thing. Plants, for example, which as a rule have a 
white flower, frequently show deviations into the blue or 
red. Now, supposing the gardener wishes to obtain the red 
colour in a plant usually producing white flowers, he will 
very carefully, from among the many different individuals 
which are the descendants of one and the same seed-plant, se- 
lect those which most distinctly show a reddish tint, and sow 
them exclusively, in order to produce new individuals of the 
same kind. He would cast aside and no longer cultivate 
the other seedlings which show a white or less distinct 
red colour. He will propagate exclusively the individual 
plants whose blossoms show the red most markedly, and he 
will sow the seeds produced by these selected plants. From 
the seedlings of this second generation, he will again care- 
fully select those in which the red, which is now visible in 
the majority of them, is most distinctly displayed. If 
such a selection is carried on during a series of six or ten 
generations, and if the flower which shows the deepest red 
is most carefully selected, the gardener in the sixth or tenth 
generation will obtain the desired plants with flowers of a 
pure red. 



The farmer wishing to breed a special race of animals, for 
example, a kind of sheep distinguished by particularly fine 
wool, proceeds in the same manner. The only process 
applied in the improvement of wool consists in this, that the 
farmer with the greatest care and perseverance selects from 
a whole flock of sheep those individuals which have the 
finest wool. These only are used in breeding, and among 
the descendants of these selected sheep, those again are 
chosen which have the finest wool, etc. If this careful 
selection is carried on through a series of generations, the 
selected breeding-sheep are in the end distinguished by a 
wool which differs very strikingly from the wool of the 
original parent, and this is exactly the advantage which 
the breeder desired. 

The differences of the individuals that come into considera- 
tion in this artificial selection are very slight. An ordinary 
unpractised man is unable to discover the exceedingly 
minute differences of individuals which a practised breeder 
perceives at the first glance. The business of a breeder is 
not easy; it requires an exceedingly sharp eye, great 
patience, and an extremely careful manner of treating the 
organisms to be bred. In each individual generation, the 
differences of individuals are perhaps not seen at all by the 
uninitiated ; but by the accumulation of these minute 
differences during a series of generations, the deviation from 
the original form becomes in the end very great. It becomes 
so great that the artificially produced form may in the end 
differ far more from the original form than do two so- 
called "good species" in their natural state. The art of 
breeding has now made such progress, that man can often at 
discretion produce certain peculiarities in cultivated species 


of animals and plants. To practised gardeners and farmers, 
you may give distinct commissions, and say, for example, 
I wish to have this species of plant with this or that colour, 
and with this or that shape. Where breeding has reached 
the perfection which it has attained in England, gardeners 
and farmers are frequently able to furnish to order the 
desired result within a definite period, that is, at the end of 
a number of generations. Sir John Sebright, one of the most 
experienced English pigeon-breeders, could assert that in 
three years he would produce any form of feather, but that 
he required six years to obtain any desired form of the head 
and beak. In the process of breeding the merino-sheep of 
Saxony, the animals are three times placed on a table beside 
one another, and most carefully compared and studied- 
Each time only the best sheep with the finest wool are 
selected, so that in the end, out of a great multitude, there 
remain only some few animals, but their wool is exquisitely 
fine, and only these last are used in breeding. We see, 
therefore, that the causes through which, in artificial 
breeding, great effects are produced, are unusually simple, 
and these great effects are obtained simply by accumulating 
the differences which in themselves are very insignificant,. 
and become surprisingly increased by a continually repeated 

Before we pass on to a comparison of this artificial with 
natural breeding, let us see what natural qualities of the 
organisms are made use of by the artificial breeder or 
cultivator. We can trace all the different qualities which 
here come into play to physiological fundamental qualities of 
the organism, which are common to all animals and plants, 
and are most closely connected with the functions of 


'propagation and nutrition. These two fundamental quali- 
ties are transmissivity, or the capability of transmitting by 
inheritance, and mutability, or the capability of adaptation. 
The breeder starts from the fact that all the individuals of 
one and the same species are different, though in a very 
slight degree, a fact which is as true of organisms in a wild 
as in a cultivated state. If you look about you in a forest 
consisting of only a single species of tree, for example of 
beech, you will certainly not find in the whole forest two 
trees of this kind which are absolutely identical or perfectly 
equal in the form of their branches, the number of their 
branches and leaves, blossoms and fruits. Special differences 
occur everywhere, just as in the case of men. There are 
no two men who are absolutely identical, perfectly equal in 
size, in the formation of their faces, the number of their 
hairs, their temperament, character, etc. The very same is 
true of individuals of all the different species of animals and 
plants. It is true that in most organisms the differences are 
very trifling to the eye of the uninitiated. Everything 
here essentially depends on the exercise of the faculty of 
•discovering these often very minute differences of form. The 
shepherd, for example, knows every individual of his flock, 
solely by accurately observing their features, while the 
uninitiated are incapable of distinguishing at all the different 
individuals of one and the same flock. This fact of the 
individual difference is the extremely important foundation 
■on which the whole of man's power of breeding rests. If 
individual differences did not exist everywhere, man would 
not be able to produce a number of different varieties or 
races from one and the same original stock. We must, at 
the outset, hold fast the principle that the phenomenon is 


quite universal ; we must necessarily assume it even where,, 
with the imperfect capabilities of our senses, we are unable 
to discover diiferences. Among the higher plants (the 
phanerogams, or flower-plants), where the individual stocks 
show such numerous differences in the number of branches or 
leaves, and in the formation of the stem and branches, we 
can almost always easily perceive these differences. But 
this is not the case in the lower plants, such as mosses, 
algse, fungi, and in most animals, especially the lower ones. 
The distinction of all the individuals of one species is here, 
for the most part, extremely difficult or altogether impossible. 
But there is no reason for ascribing individual differences only 
to those organisms in which we can perceive them at once. 
We may, on the contrary, with full certainty assume such 
individuality as a universal quality of all organisms, and we 
can do this all the more surely since we are able to trace the 
mutability of individuals to the mechanical conditions of 
nutrition. We can show that by influencing nutrition we 
are able to produce striking individual differences where they 
would not exist if the conditions of nutrition had not been 
altered. The many complicated conditions of nutrition are 
never absolutely identical in two individuals of a species. . 

Now, just as we see that the mutability or capability of 
adaptation has a causal connection with the general rela- 
tions of nutrition in animals and plants, so too we find the 
second fundamental phenomenon of life, with which we are 
here concerned, namely, the capability of transmitting by 
inheritance, to have a direct connection with the phenome- 
non of propagation. The second thing that a farmer or 
gardener does in artificial breeding, after he has selected, 
and has consequently availed himself of the mutability, is 


to endeavour to hold fast and develop the modified forms by- 
Inheritance. He starts from the universal fact that children 
resemble their parents, that "the apple does not fall far 
from the tree." This phenomenon of Inheritance has hitherto 
been scientifically examined only to a very small extent, 
which may partly arise from the fact that the phenomenon 
is of such everyday occurrence. Every one considers it 
quite natural that every species should produce its like ; 
that a horse should not suddenly produce a goose, or a goose 
a frog. We are accustomed to look upon these everyday 
occurrences of Inheritance as self-evident. But this phe- 
nomenon is not so simply self-evident as it appears at 
first sight, and in the examination of Inheritance the fact is 
very frequently overlooked that the different descendants, 
derived from one and the same parents, are in reality never 
quite identical, and also never absolutely like the parents, 
but are always slightly different. We cannot formulate the 
principle of Inheritance, as "Like produces like," but we 
must limit the expression to " Similar things produce 
similar things." The gardener, as well as the farmer, 
avails himself of the fact of Inheritance in its widest 
form, and indeed with special regard to the fact that not 
only those qualities of organisms are transmitted by 
inheritance which they have inherited from their parents, 
but those also which they themselves have acquired. This 
is an important point upon which very much depends. An 
organism can transmit to its descendants not only those 
qualities of form, colour, and size which it has inherited 
from its parents, but it can also transmit changes of these 
qualities, which it has acquired during its own life through 
the influence of outward circumstances, such as climate, 
nourishment, training, etc. 


These are the two fundamental qualities of animals and 
plants of which the breeder must avail himself in order to 
produce new forms. The theoretical principle of breeding 
is, indeed, extremely simple, but in detail the practical appli- 
cation of this simple principle is difficult and immensely 
complicated. A thoughtful breeder, acting according to 
a definite plan, must understand the art of correctly esti- 
mating, in every case, the general interaction between the 
two fundamental qualities of heirship and mutability. 

Now, if we examine the real nature of those two impor- 
tant properties of life, we find that we can trace them, like 
all physiological functions, to physical and chemical causes, 
to the properties and the phenomena of motion of those 
substances of which the bodies of animals and plants 
consist. As we shall hereafter have to show in the more 
accurate consideration of these two functions, the trans- 
mission by Inheritance, if we express ourselves quite 
generally, is essentially dependent upon the material con- 
tinuity and partial identity of the matter in the producing 
and produced organism, the parents and the child. In 
every act of breeding a certain quantity of protoplasm or 
albuminous matter is transferred from the parents to the 
child, and along with it there is transferred the individually 
peculiar molecular motion. These molecular phenomena of 
motion in the protoplasm, which call forth the phenomena 
of life, and are their active and true cause, differ more or 
less in all living individuals ; they are of infinite variety. 

Adaptation, or transmutation is, on the other hand, 
essentially the consequence of material influences, which the 
substance of the organism experiences from the material 
surrounding it, — in the widest sense of the word from the 


conditions of life. The external influences of the latter are 
communicated to the individual parts of the body by the 
molecular processes of nutrition. In every act of Adaptation 
the individual molecular motion of the protoplasm, peculiar 
to each part, disturbs and modifies the whole individual, or 
part of it, by mechanical, physical, or chemical influences. 
The innate, inherited vital actions of the protoplasm — that is, 
the molecular phenomena of motion of the smallest albu- 
minous particles — are therefore more or less modified by it. 
The phenomenon of Adaptation, or transmutation, depends 
therefore upon the material influence which the organism 
experiences from its surroundings, or its conditions of 
existence ; while the transmission by Inheritance is due 
to the partial identity of the producing and produced 
organism. These are the real, simple, mechanical founda- 
tions of the artificial process of breeding. 

Now Darwin asked himself, Does there exist a similar 
process of selection in nature, and are there forces in nature 
which take the place of man's activity in artificial selection ? 
Is there a natural tendency among wild animals and plants 
which acts selectingly, in a similar manner to the artificial 
selection practised by the designing will of man? All 
here depended upon the discovery of such a relation, and 
Darwin succeeded in this so satisfactorily, that we con- 
sider his theory of selection completely sufficient to 
explain, mechanically, the origin of the wild species of 
animals and plants. That relation which in free 
nature influences the forms of animals and plants, by 
selecting and transforming them, is called by Darwin 
the " Struggle for Existence." 

The " Struggle for Existence " has rapidly become a 


watchword of the day. Yet this designation is, perhaps, in 
many respects not very happily chosen, and the phenomena 
might probably have been more accurately described as 
" Competition for the Means of Subsistence." For under the 
name of "Struggle for Life," many relations are compre- 
hended which properly and strictly speaking do not belong- 
to it. As we have seen from the letter inserted in the 
last chapter, Darwin arrived at the idea of the " Struggle 
for Existence " from the study of Malthus' book " On the 
Conditions and the Consequences of the Increase of Popula- 
tion." It was proved in that important work, that the 
number of human beings, on the average, increases in a 
geometrical progression, while the amount of articles of food 
increase only in an arithmetical progression. This dispro- 
portion gives rise to a number of inconveniences in the 
human community, which cause among men a continual 
competition to obtain the necessary means of life, which 
do not suffice for all. 

Darwin's theory of the struggle for life is, to a certain 
extent, a general application of Malthus' theory of popula- 
tion to the whole of organic nature. It starts from the 
consideration that the number of possible organic indi- 
viduals which might arise from the germs produced, is far 
greater than the number of actual individuals which, in 
fact, do simultaneously live on the earth's surface. The 
number of possible or potential individuals is given us by 
the number of the eggs and organic germs produced by 
organisms. The number of these germs, from each of which, 
under favourable circumstances, an individual might arise, 
is very much larger than the number of real or actual 
individuals— that is, of those that really arise from these 

VOL. I. M 


germs, come into life, and propagate themselves. By far 
the greater number of germs perish in the earliest stage of 
life, and it is only some favoured organisms which manage to 
develop, and actually survive the first period of early youth, 
and finally succeed in propagating themselves. This import- 
ant fact is easily proved by a comparison of the number of 
eggs in a given species with the number of individuals which 
exist of this species. These numerical relations show the 
most striking contrast. There are, for example, species of 
fowls which lay great numbers of eggs, and yet are among 
the rarest of birds ; and the bird which is said to be the 
commonest (the most widely spread) of all, the stormy petrel 
(Procellaria glacialis), lays only a single egg. The relation 
is the same in other animals. There are many very rare 
invertebrate animals, which lay immense quantities of eggs ; 
and others again which produce only very few eggs, and yet 
are among the commonest of animals. Take, for example, 
the proportion which is observed among the human tape- 
worms. Each tape-worm produces within a short period 
millions of eggs, while man, in whom these tape-worms are 
lodged, forms a far smaller number of eggs, and yet for- 
tunately there are fewer tape-worms than human beings. 
In like manner, among plants there are many splendid 
orchids, which produce thousands of seeds and yet are very 
rare, and some kinds of asters (Compositae), which have but 
few seeds, are exceedingly common. 

This important fact might be illustrated by an immense 
number of examples. It is evidently, therefore, not the 
number of actually existing germs which indicates the num- 
ber of individuals which afterwards come into life and 
maintain themselves in life ; but rather the case is this, 


"that the number of adult individuals is limited by other 
circumstances, especially by the relations in which the 
organism stands to its organic and inorganic surroundings. 
Every organism, from the commencement of its existence, 
struggles with a number of hostile influences : it struggles 
against animals which feed on it, and to which it is thenatural 
food, against animals of prey and parasites ; it struggles 
against inorganic influences of the most varied kinds, against 
temperature, weather, and other circumstances ; but it also 
struggles (and this is much the most important !), above all, 
against organisms most like and akin to itself. Every 
individual, of every animal and vegetable species, is engaged 
in the fiercest competition with every other individual of 
the same species which fives in the same place with it. In 
the economy of nature the means of subsistence are 
nowhere scattered in abundance, but are very limited, 
and far from sufficient for the number of organisms which 
might develop from the germs produced. Therefore the 
young individuals of most species of animals and vegetables 
must have hard work in obtaining the means of subsist- 
ence ; this necessarily causes a competition among them in 
■order to obtain the indispensable supplies of life. 

This great competition for the necessaries of life goes on 
-everywhere and at all times, among human beings and 
animals as well as among plants ; in the case of the latter 
this circumstance, at first sight, is not so clearly apparent. 
If we examine a field which is richly sown with wheat, 
we can see that of the numerous young plants (perhaps 
some thousands) which shoot up on a limited space, only a 
very small proportion preserve themselves in life. A com- 
petition takes place for the space of ground which each plant 


requires for fixing its root, a competition for sunlight and 
moisture. And in the same manner we find that, among all 
animal species, all the individuals of one and the same species 
compete with one another to obtain these indispensable 
means of life, or the conditions of existence in the wide 
sense of the word. They are equally indispensable to all, 
but really fall to the lot of only a few — " Many are called, 
but few are chosen." The fact of the great competition is- 
quite universal. You need only to cast a glance at human 
society, where this competition exists everywhere, and in 
all the different branches of human activity. Here, too,, 
a struggle is brought about by the free competition of the 
different labourers of one and the same class. Here too,. 
as everywhere, this competition benefits the thing, or the 
work, which is the object of competition. The greater and 
more general the competition, the more quickly improve- 
ments and inventions are made in the branch of labour, and 
the higher is the grade of perfection of the labourers them- 

The position of the different individuals in this struggle 
for life is evidently very unequal. Starting from the 
inequality of individuals, which is a recognized fact, we 
must in all cases necessarily suppose that all the individuals 
of one and the same species do not have equally favourable 
prospects. Even at the beginning they are differently placed 
in this competition by their different strengths and abilities,, 
independently of the fact that the conditions of existence 
are different, and act differently at every point of the earth's 
surface. We evidently have an infinite combination of in- 
fluences, which, together with the original inequality of the 
individuals during the competition for the conditions of 


'existence, favour some individuals and prejudice others. The 
favoured individuals will gain the victory over the others, 
and while the latter perish more or less early, without leav- 
ing any descendants, the former alone will be able to survive 
and finally to propagate the species. As, therefore, it is 
clear that in the struggle for life the favoured individuals 
succeed in propagating themselves, we shall (even as the re- 
sult of this relation) perceive in the next generation differ- 
ences from the preceding one. Some individuals of this 
second generation, though perhaps not all of them, will, 
by inheritance, receive the individual advantage by which 
their parents gained the victory over their rivals. 

But now — and this is a very important law of inheritance 
— if such a transmission of a favourable character is con- 
tinued through a series of generations, it is not simply trans- 
mitted in the original manner, but it is constantly increased 
and strengthened, and in a last generation it attains a 
strength which distinguishes this generation very essentially 
from the original parent. Let us, for example, examine a 
number of plants of one and the same species which grow 
together in a very dry soil. As the hairs on the leaves of 
plants are very useful for receiving moisture from the air, 
and as the hairs on the leaves are very changeable, the 
individuals possessing the thickest hair on their leaves will 
have an advantage in this unfavourable locality where the 
plants have directly to struggle with the want of water, and 
in addition to this have to compete with one another for 
the possession of what little water there may be. These 
alone hold out, while the others possessing less hairy leaves 
perish ; the more hairy ones will be propagated, and their 
descendants will, on the average, be more distinguished by 


their thick and strong hairs than the individuals of the first 
generation. If this process is continued for several genera- 
tions in one and the same locality, there will arise at last 
such an increase of this characteristic, such an increase of 
the hairs on the surface of the leaf, that an entirely new- 
species seems to present itself. It must here be observed, 
that in consequence of the interactions of all the parts of 
every organism, generally one individual part cannot be 
changed without at the same time producing changes in other 
parts. If, for instance, in our imaginary example, the number 
of the hairs on the leaves is greatly increased, a certain 
amount of nourishment is thereby withdrawn from other 
parts ; the material which might be employed to form 
flowers or seeds is diminished, and a smaller size of the 
flower or seed will then be the direct or indirect consequence 
of the struggle for life, which in the first place only pro- 
duced a change in the leaves. Thus the struggle for life, in 
this instance, acts as a means of selecting and transforming. 
The struggle of the different individuals to obtain the 
necessary conditions of existence, or, taking it in its widest 
sense, the inter-relations of organisms to the whole of their 
surroundings, produce mutations of form such as are pro- 
duced in the cultivated state by the action of man's selection. 
This agency will perhaps appear at first sight small and 
insignificant, and the reader will not be inclined to concede 
to the action of such relations the weight which it in reality 
possesses. I must therefore find space in a subsequent 
chapter to put forward further examples of the immense 
and far-reaching power of transformation exhibited in 
natural selection. For the present I will confine myself to 
simply placing side by side the two processes of artificial 


and natural selection, and clearly explaining the agreement 
and the differences of the two. 

Both natural and artificial selection are quite simple 
natural, mechanical relations of life, which depend upon the 
interaction of two physiological functions, namely, on Adap- 
tation and Inheritance, functions which, as such, must again 
be traced to physical and chemical properties of organic 
matter. The difference between the two forms of selection 
consists in this : in artificial selection the will of man makes 
the selection according to a, plan, whereas in natural selection, 
the struggle for life (that universal inter-relation of organ- 
isms) acts without a plan, but otherwise produces quite the 
same result, namely, a selection of a particular kind of indi- 
viduals for propagation. The alterations produced by artifi- 
cial selection are turned to the advantage of those %vho make 
the selection ; in natural selection, on the other hand, to the 
advantage of the selected organism. 

These are the most essential differences and agreements of 
the two modes of selection ; it must, however, be further 
observed that there is another difference, viz. in the duration of 
time required for the two processes of selection. Man in his 
artificial selection can produce very important changes in a 
very short time, while in natural selection similar results are 
obtained only after a much longer time. This arises from 
the fact that man can make his selection with much greater 
care. Man is able with the greatest nicety to pick out indi- 
viduals from a large number, drop the others, and to employ 
only the privileged beings for propagation, which is not the 
case in natural selection. In natural conditions, besides the 
privileged individuals which first succeed in propagating 
themselves, some few or many of the less distinguished indi- 


viduals will propagate themselves by the side of the former. 
Moreover, man can prevent the crossing of the original and 
the new form, which in natural selection is often unavoidable. 
If such a crossing, that is, a sexual connection, of the new 
variety with the original forms takes place, the offspring 
thereby produced generally returns to the original character. 
In natural selection, such a crossing can be avoided only 
when the new variety by migration separates from the origi- 
nal and isolates itself. 

Natural selection therefore acts much more slowly; it 
requires much longer periods than the artificial process of 
selection. But it is an essential consequence of this differ- 
ence, that the product of artificial selection disappears much 
more easily, and that the new form returns rapidly to the 
earlier one, which is not the case in natural selection. The 
new species arising from natural selection maintain them- 
selves much more permanently, and return much less easily 
to the original form, than is the case with products of artifi- 
cial selection, and accordingly maintain themselves during a 
much longer time than the artificial races produced by man. 
But these are only subordinate differences, which are ex- 
plained by the different conditions of natural and artificial 
selection, and in reality are connected only with differences 
in the duration of time. The nature of the transformation 
and the means by which it is produced are entirely the 
same in both artificial and natural selection. (Gen. Morph. 
ii. 248). 

The thoughtless and narrow-minded opponents of Darwin 
are never tired of asserting that his theory of selection is 
a groundless conjecture, or at least an hypothesis which has 
yet to be proved. That this assertion is completely un- 


founded, may be perceived even from the outlines of the doc- 
trine of selection which have just been discussed. Darwin 
assumes no kind of unknown forces of nature, nor hypothetical 
■conditions, as the acting causes for the transformation of organic 
forms, but solely and simply the universally recognized vital 
■activities of all organisms, which we term Inheritance and 
Adaptation. Every naturalist acquainted with physiology 
knows that these two phenomena are directly connected 
with the functions of propagation and nutrition, and, like all 
other phenomena of life, are purely mechanical processes of 
nature, that is, they depend upon the molecular phenomena 
of motion in organic matter. That the interaction of these 
two functions effect a continual, slow transmutation of or- 
ganic forms, is a necessary result of the struggle for exist- 
ence. But this, again, is no more a hypothetical relation, nor 
one requiring a proof, than is the interaction of Inheritance 
and Adaptation. The struggle for life is a mathematical 
necessity, arising from the disproportion between the limited 
number of places in nature's household, and the excessive 
number of organic germs. The origin of new species is 
moreover greatly favoured by the active or passive migra- 
tions of animals and plants, which takes place everywhere 
and at all times, without being, however, entitled to rank 
as necessary agents in the process of natural selection. 

The origin of new species by natural selection, or, what 
is the same thing, by the interaction of Inheritance and 
Adaptation in the struggle for life, is therefore a mathe- 
matical necessity of nature which needs no further proof. 
Whoever, in spite of the present state of our knowledge, 
still seeks for proofs for the Theory of Selection, only 
.shows that he either does not thoroughly understand the 


theory, or is not sufficiently acquainted with the biological 
facts — has not the requisite amount of experimental know- 
ledge in Anthropology, Zoology, and Botany. 

If, as we maintain, natural selection is the great active 
cause which has produced the whole wonderful variety of 
organic life on the earth, all the interesting phenomena of 
human life must also be explicable from the same cause. 
For man is after all only a most highly-developed vertebrate 
animal, and all aspects of human life have their parallels, or, 
more correctly, their lower stages of development in the 
animal kingdom. The whole history of nations, or what is 
called " Universal History," must therefore be explicable by 
means of "natural selection," — must be a physico-chemical 
process, depending upon the interaction of Adaptation and 
Inheritance in the struggle for life. And this is actually 
the case. We shall give further proofs of this later on. 

It appears of interest here to remark that not only 
natural selection, but also artificial selection exercises its 
influence in many ways in universal history. A remark- 
able instance of artificial selection in man, on a great 
scale, is furnished by the ancient Spartans, among whom, 
in obedience to a special law, all newly-born children 
were subject to a careful examination and selection. All 
those that were weak, sickly, or affected with any bodily 
infirmity, were killed. Only the perfectly healthy and strong 
children were allowed to live, and they alone afterwards pro- 
pagated the race. By this means, the Spartan race was not 
only continually preserved in excellent strength and vigour, 
but the perfection of their bodies increased with every 
generation. No doubt the Spartans owed their rare degree 
of masculine strength and rough heroic valour (for which 


they are eminent in ancient history) in a great measure to 
this artificial selection. 

Many tribes also among the Red Indians of North- 
America (who at present are succumbing in the struggle- 
for life to the superior numbers of the white intruders, in 
spite of a most heroic and courageous resistance) owe their 
rare degree of bodily strength and warlike bravery to a 
similar careful selection of the newly-born children. Among 
them, also, all children that are weak or affected with any 
infirmity are immediately killed, and only the perfectly 
strong individuals remain in life, and propagate the race. 
That the race becomes greatly strengthened, in the course 
of very many generations, by this artificial selection cannot 
in itself be doubted, and is sufficiently proved by many well 
known facts. 

The opposite of this artificial selection of the wild Red- 
skins and the ancient Spartans is seen in the individual 
selection which is universally practised in our modern mili- 
tary states, for the purpose of maintaining standing armies, 
and which, under the name of military selection, we may 
conveniently consider as a special form of selection. Un- 
fortunately, in our day, militarism is more than ever promi- 
nent in our so-called " civilization " ; all the strength and 
all the wealth of flourishing civilized states are squandered 
on its development; whereas the education of the young, 
and public instruction, which are the foundations of the 
true welfare of nations and the ennobling of humanity, are 
neglected and mismanaged in a most pitiable manner. And 
this is done in states which believe themselves to be the 
privileged leaders of the highest human intelligence, and to 
stand at the head of civilization. As is well known, in 


order to increase the standing army as much as possible, all 
healthy and strong young men are annually selected by a 
strict system of recruiting. The stronger, healthier, and 
more spirited a youth is, the greater is his prospect of being- 
killed by needle-guns, cannons, and other similar instru- 
ments of civilization. All youths that are unhealthy, weak, 
■or affected with infirmities, on the other hand, are spared by 
the "military selection," and remain at home during the 
war, marry, and propagate themselves. The more useless, 
the weaker, or infirmer the youth is, the greater is his pros- 
pect of escaping the recruiting officer, and of founding a 
family. While the healthy flower of youth dies on the 
battle-field, the feeble remainder enjoy the satisfaction of 
reproduction and of transmitting all their weaknesses and 
infirmities to their descendants. According to the laws of 
transmission by inheritance, there must necessarily follow in 
each succeeding generation, not only a further extension, 
but also a more deeply-seated development of weakness of 
body, and what is inseparable from it, a condition of mental 
weakness also. This and other forms of artificial selection 
practised in our civilized states sufficiently explain the sad 
fact that, in reality, weakness of the body and weakness of 
•character are on the perpetual increase among civilized 
nations, and that, together with strong, healthy bodies, free 
and independent spirits are becoming more and more scarce. 
To the increasing enervation of modern civilized nations, 
which is the necessary consequence of military selection, 
there is further added another eviL The progress of modern 
medical science, although still little able really to cure 
•diseases, yet possesses and practises more than it used to 
-do the art of prolonging life dming lingering, chronic 


diseases for many years. Such ravaging evils as consump- 
tion, scrofula, syphilis, and also many forms of mental dis- 
orders, are transmitted by inheritance to a great extent, 
and transferred by sickly parents to some of their children, 
or even to the whole of their descendants. Now, the longer 
the diseased parents, with medical assistance, can drag on 
their sickly existence, the more numerous are the descend- 
ants who will inherit incurable evils, and the greater will 
be the number of individuals, again, in the succeeding gene- 
ration, thanks to that artificial " medical selection," whc- 
will be infected by their parents with lingering, hereditary 

If any one were to venture the proposal, after the ex- 
amples of the Spartans and Redskins, to kill, immediately 
upon their birth, all miserable, crippled children to whom 
with certainty a sickly life could be prophesied, instead of 
keeping them in life injurious to them and to the race, 
our so-called "humane civilization" would utter a cry of 
indignation. But the same "humane civilization" thinks 
it quite as it should be, and accepts without a murmur, that 
at the outbreak of every war (and in the present state of 
civilized life, and in the continual development of standing- 
armies, wars must naturally become more frequent) hundreds 
and thousands of the finest men, full of youthful vigour, are 
sacrificed in the hazardous game of battles. The same 
" humane civilization " at present praises the abolition of 
capital punishment as a " liberal measure ! " And yet 
capital punishment for incorrigible and degraded criminals 
is not only just, but also a benefit to the better portion of 
mankind ; the same benefit is done by destroying luxuriant 
weeds, for the prosperity of a well cultivated garden. As 


by a careful rooting out of weeds, light, air, and ground is 
gained for good and useful plants, in like manner, by the 
indiscriminate destruction of all incorrigible criminals, not 
only would the struggle for life among the better portion of 
mankind be made easier, but also an advantageous artificial 
process of selection woidd be set in practice, since the possi- 
bility of transmitting their injurious qualities by inheritance 
would be taken from those degenerate outcasts. 

Against the injurious influence of artificial military and 
medical selection, we fortunately have a salutary counter- 
poise, in the invincible and much more powerful influence 
of natural selection, which prevails everywhere. For in 
the life of man, as well as in that of animals and plants, this 
influence is the most important transforming principle, and 
the strongest lever for progress and amelioration. The 
result of the struggle for life is that, in the long run, that 
which is better, because more perfect, conquers that which 
is weaker and imperfect. In human life, however, this 
struggle for life will ever become more and more of an 


intellectual struggle, not a struggle with weapons of murder. 
The organ which, above all others, in man becomes more 
perfect by the ennobling influence of natural selection, is 
the brain. The man with the most perfect understanding, 
not the man with the best revolver, will in the long run be 
victorious ; he will transmit to his descendants the qualities 
of the brain which assisted him in the victory. Thus then 
we may justly hope, in spite of all the efforts of retrograde 
forces, that the progress of mankind towards freedom, and 
thus to the utmost perfection, will, by the happy influence 
of natural selection, become more and more certain. 




Universality of Inheritance and Transmission by Inheritance. — Special 
Evidences of the same. — Human Beings with four, six, or seven 
Fingers and Toes. — Porcupine Men. — Transmission of Diseases, espe- 
cially Diseases of the Mind. — Original Sin. — Hereditary Monarchies. — 
Hereditary Aristocracy. — Hereditary Talents and Mental Qualities.- — 
Material Causes of Transmission by Inheritance. — Connection between 
Transmission by Inheritance and Propagation. — Spontaneous Genera- 
tion and Propagation. — Non-sexual or Monogonons Propagation. — Propa- 
gation by Self-Division. — Monera and Amoeba3. — Propagation by the 
formation of Buds, by the formation of Germ-Buds, by the formation of 
Germ-Cells. — Sexual or Amphigonous Propagation. — Formation of 
Hermaphrodites. — Distinction of Sexes, or Gonochorism. — Virginal 
Breeding, or Parthenogenesis. — Material Transmission of Peculiarities 
of both Parents to the Child by Sexual Propagation. — Difference 
between Transmission by Inheritance in Sexual and in Asexual 

The reader has, in the last chapter, become acquainted 
with natural selection according to Darwin's theory, as the 
constructive force of nature which produces the different 
forms of animal and vegetable species. By natural selection 
we understand the interaction which takes place in the 
struggle for life between the transmission by inheritance 
and the mutability of organisms, between two physiological 
functions which are innate in all animals and plants 


and which may be traced to other processes of life — the 
functions of propagation and nutrition. All the different 
forms of organisms, which people are usually inclined to 
look upon as the products of a creative power, acting for a 
definite purpose, we, according to the Theory of Selection, 
can conceive as the necessary productions of natural selec- 
tion, working without a purpose, — as the unconscious inter- 
action between the two properties of Mutability and 
Hereditivity. Considering the importance which accordingly 
belongs to these vital properties of organisms, we must 
examine them a little more closely, and employ a chapter 
with the consideration of Transmission by Inheritance. 
(Gen. Morph. ii. 170-191). 

Strictly speaking, we must distinguish between Heredi- 
tivity (Transmissivity) and Inheritance (Transmission). 
Hereditivity is the power of transmission, the capability of 
organisms to transfer their peculiarities to their descendants 
by propagation. Transmission by Inheritance, or Inheritance 
simply, on the other hand, denotes the exercise of the 
capability, the actual transmission. 

Hereditivity and Transmission by Inheritance are such 
universal, everyday phenomena, that most people do not 
heed them, and but few are inclined to reflect upon the 
operation and import of these phenomena of life. It is 
generally thought quite natural and self-evident that every 
organism shordd produce its like, and that children should 
more or less resemble their parents. Heredity is usually 
only taken notice of and discussed in cases relating 
to some special peculiarity, which appears for the first 
time in a human individual without having been inherited, 
and then is transmitted to his descendants. It shows 


itself in a specially striking manner in the case of certain 
diseases, and in unusual and irregular (monstrous) devia- 
tions from the usual formation of the body. 

Among these cases of the inheritance of monstrous devi- 
ations, those are specially interesting which consist in an 
abnormal increase or decrease of the number five in the fin- 
gers or toes of man. It is not unfrequently observed in 
families through several generations, that individuals have six 
fingers on each hand, or six toes on each foot. Less frequent 
is the number of four or seven fingers or toes. The unusual 
formation arises at first from a single individual who, from 
unknown causes, is born with an excess of the usual number 
of fingers and toes, and transmits these, by inheritance, to a 
portion of his descendants. In one and the same family it 
has happened that, throughout three, four, or more genera- 
tions, individuals have possessed six fingers and toes. In a 
Spanish family there were no less than forty individuals 
distinguished by this excess. The transmission of the sixth 
finger or toe is not permanent or enduring in all cases, be- 
cause six-fingered people always intermarry again with 
those possessing five fingers. If a six-fingered family were 
to propagate by pure in-breeding, if six-fingered men were 
always to marry six-fingered women, this characteristic 
woidd become permanent, and a special six-fingered human 
race would arise. But as six-fingered men usually marry 
five-fingered women, and vice versd, their descendants for 
the most part show a very mixed numerical relation, and 
.finally, after the course of some generations, revert again to 
the normal number of five. Thus, for example, among eight 
children of a six-fingered father and a five-fingered mother, 
two children may have on both hands and feet six fingers 
vol. I. n 


and toes, four children may have a mixed number, and two 
children may have the usual number of five on both hands 
and feet. In a Spanish family, each child except the 
youngest had the number six on both hands and feet ; the 
youngest, only, had the usual number on both hands and feet, 
and the six-fingered father of the child refused to recognize 
the last one as his own. 

The power of inheritance, moreover, shows itself very 
strikingly in the formation and colour of the human skin 
and hair. It is well known how exactly the nature of the 
complexion in many families — for instance, a peculiar soft 
or rough skin, a peculiar luxuriance of the hair, a peculiar 
colour and largeness of the eyes — is transmitted through 
many generations. In like manner, peculiar local growths 
or spots on the skin, the so-called moles, freckles, and other 
accumulations of pigment which appear in certain places, are 
frequently transmitted through several generations so 
exactly, that in the descendants they appear on the same 
spots on which they existed in the parents. The porcupine 
men of the Lambert family, who lived in London last cen- 
tury, are especially celebrated. Edward Lambert, born in 
1717, was remarkable for a most unusual and monstrous 
formation of the skin. His whole body was covered with a 
horny substance, about an inch thick, which rose in the 
form of numerous thorn-shaped and scale-like processes, 
more than an inch long. This monstrous formation of the 
outer skin, or epidermis, Was transmitted by Lambert to his 
sons and grandsons, but not to his granddaughters. The 
transmission in this instance remained in the male line, as 
is often the case. In like manner, an excessive develop- 
ment of fat in certain parts of the body is often transmitted 


only in the female line. I scarcely need call to mind how 
exactly the characteristic formation of the face is transmitted 
by inheritance ; sometimes it remains within the male, some- 
times within the female line ; sometimes it is blended in both. 
The phenomena of transmission by inheritance of patho- 
logical conditions, especially of the different forms of human 
diseases, are very instructive and generally known. Diseases 
of the respiratory organs, the glands, and of the nervous 
system, are specially liable to be transmitted by inheritance. 
Very frequently there suddenly appears in an otherwise 
healthy family a disease until then unknown among them ; 
it is produced by external causes, by conditions of life causing 
disease. This disease, brought about in an individual by 
external cause, is propagated and transmitted to his descend- 
ants, and some or all of them then suffer from the same 
disease. In case of diseases of the lungs, for instance in 
consumption, this sad transmission by inheritance is well 
known, and it is the same with diseases of the liver, with 
syphilis, and diseases of the mind. The latter are specially 
interesting. Just as peculiar characteristic features of man 
— pride, ambition, frivolity, etc. — are transmitted to the 
descendants strictly by inheritance, so too are the peculiar 
abnormal manifestations of mental activity, which are 
usually called fixed ideas, despondency, imbecility, and 
generally "diseases of the mind." This distinctly and 
irrefragably shows that the soul of man, just as the soul 
of animals, is a . purely mechanical activity, the sum of 
the molecular phenomena of motion in the particles of the 
brain, and that it is transmitted by inheritance, together 
with its substratum, just as every other quality of the body 
is materially transmitted by propagation. 


When this exceedingly important and undeniable fact is 
mentioned, it generally causes great offence, and yet in 
reality it is silently and universally acknowledged. For 
upon what else do the ideas of " hereditary sin," " hereditary 
wisdom," and " hereditary aristocracy," etc., rest than upon 
the conviction that the quality of the human mind is trans- 
mitted by propagation — that is, by a purely material pro- 
cess — through the body, from the parents to the descendants ? 
The recognition of this great importance of transmission by 
inheritance is shown in a number of human institutions, as 
for example, among many nations in the division into castes, 
such as the castes of warriors, castes of priests, and castes of 
labourers, etc. It is evident that the institution of such 
castes originally arose from the notion of the great import- 
ance of hereditary distinctions possessed by certain families, 
which it was presumed would always be transmitted 
by the parents to the children. The institution of an 
hereditary aristocracy and an hereditary monarchy is 
to be traced to the notion of such a transmission of special 
excellencies. However, it is unfortunately not only virtues, 
but also vices that are transmitted and accumulated by 
inheritance ; and if, in the history of the world, we compare 
the different individuals of the different dynasties, we shall 
everywhere find a great number of proofs of the transmission 
of qualities by inheritance, but fewer of transmissions of 
virtues than of vices. Look only, for example, at the Roman 
emperors, at the Julii and the Claudii, or at the Bourbons in 
France, Spain, and Italy ! 

In fact, scarcely anywhere could we find such a number 
of striking examples of the remarkable transmission of 
bodily and mental features by inheritance, as in the history 


of the reigning houses in hereditary monarchies. This is 
specially true in regard to the diseases of the mind pre- 
viously mentioned. It is in reigning families that mental 
disorders are hereditary in an unusual degree. Thus Esquirol, 
distinguished for his knowledge of mental diseases, proved 
that the number of insane individuals in the reigning houses 
was, in proportion to the number among the ordinary popu- 
lation, as 60 to 1 ; that is, that disorders of the brain occur 
CO times more frequently in the privileged families of the 
ruling houses than among ordinary people. If equally 
accurate statistics were made of the hereditary nobility, 
the result would probably be that here also we should find 
an incomparably larger contingent of mental diseases than 
among the common, ignoble portion of mankind. This 
phenomenon can scarcely astonish us if we consider what 
injury these privileged castes inflict upon themselves by 
their unnatural, one-sided education, and by their artificial 
separation from the rest of mankind. By this means many 
dark sides of human nature are specially developed and, as 
it were, artificially bred, and, according to the laws of trans- 
mission by inheritance, are propagated through series of 
generations with ever-increasing force and dominance. 

It is sufficiently obvious from the history of nations how 
in successive generations of many dynasties, for example, 
of the princes of Saxon Thuringia and of the Medici, the 
noble solicitude for the most perfect human accomplish- 
ments in science and art were retained and transmitted 
from father to son ; and how, on the other hand, in many 
other dynasties, for centuries a special partiality for the 
pi-ofession of war, for the oppression of human freedom, and 
for other rude acts of violence, have been hereditary. In like 


manner talents for special mental activities are transmitted in 
many families for generations, as, for instance, talent for 
mathematics, poetry, music, sculpture, the investigation of 
nature, philosophy, etc. In the family of Bach there have 
been no less than twenty-two eminent musicians. Of course 
the transmission of such peculiarities of mind depends upon 
the material process of reproduction, as does the transmission 
of mental qualities in general. In this case again, the vital 
phenomenon, the manifestation of force (as everywhere in 
nature), is directly connected with definite relations in the 
admixture of the material components of the organism. It 
is this definite proportion and molecular motion of matter 
which is transmitted by generation. 

Now, before we examine the numerous, and in some cases 
most interesting and important, laws of transmissipn by 
inheritance, let us make ourselves acquainted with the 
actual nature of the process. The phenomena of transmis- 
sion by inheritance are generally looked upon as something 
quite mysterious, as peculiar processes which cannot be 
fathomed by natural science, and the causes and actual 
nature of which cannot be understood. It is precisely in 
such a case that people very generally assume supernatural 
influences. But even in the present state of our physiology 
it can be proved with complete certainty that all the 
phenomena of inheritance are entirely natural processes, 
that they are produced by mechanical causes, and that they 
depend on the material phenomena of motion in the bodies 
of organisms, which we may consider as a part of the 
phenomena of propagation. All the phenomena of Heredity 
and the laws of Transmission by Inheritance can be traced 
to the material process of Propagation. 



Every organism, every living individual, owes its exist- 
ence either to an act of unparental or Spontaneous Genera- 
tion (Generatio Spontanea Archigonia), or to an act of 
Parental Generation or Propagation (Generatio Parentalis, 
Tocogonia). In a future chapter we shall have to consider 
Spontaneous Generation, or Archigony. At present we must 
occupy ourselves with Propagation, or Tocogony, a closer 
examination of which is of the utmost importance for under- 
standing transmission by inheritance. Most of my readers 
probably only know those phenomena of Propagation which 
are seen universally in the higher plants and animals, the 
processes of Sexual Propagation, or Amphigony. The pro- 
cesses of Non-sexual Propagation, or Monogony, are much less 
generally known. The latter, however, are far more suited 
to throw light upon the nature of transmission by inherit- 
ance in connection with propagation. 

For this reason, we shall first consider only the phe- 
nomena of non-sexual or monogonic propagation (Mono- 
gonia). This appears in a variety of different forms, as for 
example, self-division, formation of buds, the formation of 
germ-cells or spores (Gen. Morph. ii. 36-58). It will 
be most instructive, first, to examine the propagation of 
the simplest organisms known to us, which we shall have 
to return to later, when considering the question of 
spontaneous generation. These very simplest of all 
organisms yet known, and which, at the same time, are the 
simplest imaginable organisms, are the Monera living in 
water ; they are very small living corpuscles, which, strictly 
speaking, do not at all deserve the name of organism. 
For the designation " organism," applied to living creatures, 
rests upon the idea that every living natural body is com- 


posed of organs, of various parts, which fit into one another 
and work together (as do the different parts of an artificial 
machine), in order to produce the action of the whole. 
During late years we have become acquainted with Monera, 
organisms which are, in fact, not composed of any organs at 
all, hut consist entirely of shapeless, simple, homogeneous 
matter. The entire body of one of these Monera, during 
life, is nothing more than a shapeless, mobile, little lump of 
mucus or slime, consisting of an albuminous combination 
of carbon. Simpler or more imperfect organisms we cannot 
possibly conceive. 

The first complete observations on the natural history 
of a Moneron (Protogenes primordialis) were made by me 
at Nice, in 1864. Other very remarkable Monera I 
examined later (1866) in Lanzarote, one of the Canary 
Islands, and in 1867 in the Straits of Gibraltar. The com- 
plete history of one of these Monera, the orange -red 
Protoniyxa aurantiaca, is represented in Plate I, and its 
explanation is given in the Appendix. I have found 
some curious Monera also in the North Sea, off the 
Norwegian coast, near Bergen. Cienkowski has described 
(1865) an interesting Moneron from fresh waters, under the 
name of Vampyrella. But perhaps the most remarkable of 
all Monera was discovered by Huxley, the celebrated 
English zoologist, and called Bathybius Hceckelii. " Bathy- 
bius " means, living in the deep. This wonderful organism 
lives in immense depths of the ocean, which are over 
12,000 — indeed, in some parts 24,000 feet below the surface, 
and which have become known to us within the last ten 
years, through the laborious investigations made by the 
English. There, among the numerous Polythalamia and 

Lii'e history of a simplest organism. 


kr\ del 

r>otomv.ra aiurintiaca 


Radiolaria which inhabit the fine calcareous mud of these 
abysses, the Bathybius is found in great quantities, some- 
times in the shape of roundish, formless lumps of mucus, 
sometimes in the form of a network of mucus, covering 
fragments of stone and other objects. Small particles of 
chalk are frequently embedded in these mucous gelatinous 
masses, and are, perhaps, products of their secretion. The 
entire body of this remarkable Bathybius consists solely of 
shapeless plasma, or protoplasm, as in the case of the other 
Monera — that is, it consists of the same albuminous com- 
bination of carbon, which in infinite modifications is found 
in all organisms, as the essential and never-failing seat of 
the phenomena of life. I have given a detailed description 
and drawing of the Bathybius and other Monera in my 
" Monographie der Moneren," 1870, 15 from which the draw- 
ing in Fig. 9 is taken. 

In a state of rest most Monera appear as small globules of 
mucus or slime, invisible, or nearly so, to the naked eye ; 
they are at most as large as a pin's head. When the 
Moneron moves itself, there are formed on the upper surface 
of the little mucous globule, shapeless, fingerlike processes, 
or very fine radiated threads ; these are the so-called false 
feet, or pseudopodia. The false feet are simple, direct 
continuations of the shapeless albuminous .mass, of which 
the whole body consists. We are unable to perceive 
different parts in it, and we can give a direct proof of the 
absolute simplicity of the semi-fluid mass of albumen, for 
with the aid of the microscope we can follow the Moneron 
as it takes in nourishment. When small particles suited 
for its nourishment — for instance, small particles of decayed 
organic bodies or microscopic plants and infusoria — acci- 


dentally come into contact with the Moneron, they remain 
hanging to the sticky semi-fluid globule of mucus, and 
here create an irritation, which is followed by a strong afflux 
of the mucous substance, and, in consequence, they become 
finally completely inclosed by it, or are drawn into the 
body of the Moneron by displacement of the several albu- 
minous particles, and are there digested, being absorbed by 
simple diffusion (endosmosis). 

Just as simple as the process of nutrition is the 'propaga- 
tion of these primitive creatures, which in reality we can 
neither call animals nor plants. All Monera propagate 
themselves only in an asexual manner by monogony ; and 
in the simplest case, by that kind of monogony which we 
place at the head of the different forms of propagation, that 
is, by self-division. When such a little globule, for example 
a Protamoeba or a Protogenes, has attained a certain size 
by the assimilation of foreign albuminous matter, it falls 
into two pieces ; a pinching in takes place, contracting the 
middle of the globule on all sides, and finally leads to the 
separation of the two halves (compare Fig. 1.). Each half 

Fig. 1. — Propagation of the simplest organism, a Moneron, by self -division. 
A. The entire Moneron, a Protamoeba. B. It falls into two halves by a 
contraction in the middle. C. Each of the two halves has separated from 
the other, and now represents an independent individual. 


then becomes rounded off, and now appears as an indepen- 
dent individual, which commences anew the simple course 
of the vital phenomena of nutrition and propagation. In 
other Monera (Vampyrella), the body in the process of 
propagation does not fall into two, but into four equal pieces, 
and in others, again (Protomonas, Protomyxa, Myxastrum), 
at once into a number of small globules of mucus, each of 
which again, by simple growth, becomes like the parent 
body. Here it is evident that the process of propagation 
is nothing but a growth of the organism beyond its own 
individual limit of size. 

The simple method of propagation of the Moneron by self- 
division is, in reality, the most universal and most widely 
spread of all the different modes of propagation ; for by the 
same simple process of division, cells also propagate them- 
selves. Cells are those simple organic individuals, a large 
number of which constitute the bodies of most organisms, 
the human body not excepted. With the exception of the 
organisms of the lowest order, which have not even the 
perfect form of a cell (Monera), or during life only repre- 
sent a single cell (many Protista and single-celled plants), 
the body of every organic individual is composed of a great 
number of cells. Every organic cell is to a certain degree 
an independent organism, a so-called " elementary organism," 
or an " individual of the first order." Every higher organ- 
ism is, in a measure, a society or a state of such variously 
shaped elementary individuals, variously developed by divi- 
sion of labour. 39 Originally every organic cell is only a 
single globule of mucus, like a Moneron, but differing from 
it in the fact that the homogeneous albuminous substance 
has separated itself into two different parts, a firmer albu- 


minous body, the cell-kernel (nucleus), and an external, 
softer albuminous body, the cell-substance or body (proto- 
plasma). Besides this, many cells later on form a third 
(frequently absent) distinct part, inasmuch as they cover 
themselves with a capsule, by exuding an outer pellicle or 
cell-membrane (membrana). All other forms of cells, besides 
these, are of subordinate importance, and are of no further 
interest to us here. 

Every organism composed of many cells was originally a 
single cell, and it becomes many-celled owing to the fact 
that the original cell propagates itself by self-division, and 
that the new individual cells originating in this manner 
remain together, and by division of labour form a commu- 
nity or a state. The forms and vital phenomena of all many- 
celled organisms are merely the effect or the expression of all 
the forms and vital phenomena of all the individual cells of 
which they are composed. The egg, from which most ani- 
mals and plants are developed, is a simple cell. 

Fig. 2. — Propagation of a single-celled organism, Amoeba sphseroooccus, 
by self -division. A. The enclosed Amoeba, a simple globular cell consisting of 
a lump of protoplasm (c), which contains a kernel (b) and a kernel speck (a), 
and is surrounded by a cell-membrane or capsule. B. The free Amoeba, which 
has burst and left the cyst or cell-membrane. C. It begins to divide by its 
kernel forming two kernels, and by the cell-substance between the two 
becoming contracted. D. The division is completed by the cell-substance 
likewise falling into two halves (Da and Db). 


The single-celled organisms, that is, those which during 
life retain the form of a single cell, for example the Amoebae, 
as a ride propagate themselves in the simplest way by self- 
division. This process differs from the previously described 
self-division of the Moneron only in the fact that at the 
commencement the firmer cell-kernel (nucleus) falls into two 
halves, by a pinching in at its middle. The two young ker- 
nels separate from each ot,her and act now as two distinct 
centres of attraction upon the surrpunding softer albu- 
minous matter, that is, the cell-substance (protoplasma). By 
this process finally the latter also divides into two halves, and 
there now exist two new cells, which are like the mother cell. 
If the cell was surrounded by a membrane, this either does 
not divide at all, as in the case of egg-cleavage (Fig. 3, 4), or it 
passively follows the active pinching in of the protoplasm ; 
or, lastly, every new cell exudes a new membrane for itself. 

The non-independent cells which remain united in commu- 
nities or states, and thus constitute the body of higher or- 
ganisms, are propagated in the same manner as are inde- 
pendent single-celled organisms, for example, Amoeba (Fig. 2). 
Just as in that case, the cell with which most animals 
and plants commence their individual existence, namely, the 
egg, multiplies itself by simple division. When an ani- 
mal, for instance a mammal (Fig. 3, 4), develops out of an 

Fig. 3. — Egg of a mammal (a simple cell). 
a. The small kernel speck or nucleolus (the so- 
called germ-spot of the egg), b. Kernel or 
nucleus (the so-called germ-bladder of the egg). 
c. Cell-snbstance or protoplasm (the so-called 
yolk of the egg), d. Cell-capsule or membrane 
(membrane of the yolk) of the egg ; called in 
mammals, on account of its transparency, Mcni- 
brana pellucida. 


egg, this process of development always begins by the 
simple egg-cell (Fig. 3) forming 'an accumulation of cells 

Fig. 4. — First commencement of the development of a mammal's egg, the 
so-called " cleavage of the egg " (propagation of the egg-cell by repeated 
self-division) . A. The egg, by the formation of the first furrow, falls into 
two cells. B. These separate by division into four cells. C. The latter 
have divided into eight cells. D. By repeated division a globular accumu- 
lation of numerous cells has arisen. 

(Fig. 4) by continued self-division. The outer covering, or 
cell membrane, of the globular egg remains undivided. First, 
the cell-kernel of the egg (the so-called germinal vesicle) 
divides itself into two kernels, then follows the cell-sub- 
stance (the yolk of the egg) (Fig. 4> A). In like manner, 
the two cells, by continued self-division, separate into four 
(Fig. 4 B), these into eight (Fig. 4 C), into sixteen, thirty- 
two, etc., and finally there is produced a globular mass of 
very numerous little cells (Fig. 4 D). These now, by further 
increase and heterogeneous development (division of labour), 
gradually build up the compound many-celled organism. 
Every one of us, at the commencement of our individual 
development, has undergone the very same process as that 
represented in Fig. 4. The egg of a mammal — represented in 
Fig. 3, and its development in Fig. 4 — might as well be that 
of a man, as of an ape, dog, horse, or any other placental 


Now, when one examines this simplest form of propaga- 
tion, this self-division, it surely cannot be considered 
wonderful that the products of the division of the original 
organism should possess the same qualities as the parental 
individual. For they are parts or halves of the parental 
organism, and the matter or substance in both halves 
is the same, and as both the young individuals have 
received an equal amount and the same quality of matter 
from the parent individual, one can but consider it 
natural that the vital phenomena, the physiological qualities 
should be the same in both children. In fact, in regard to 
their form and substance, as well as to their vital phenomena, 
the two produced cells can in no respect be distinguished 
from one another, or from the mother cell. They have 
inherited from her the same nature. 

But this same simple propagation by self-division is not 
only confined to simple cells — it is the same also in the 
higher many-celled organisms; for example, in the coral 
zoophytes. Many of them which exhibit a high complexity 
of composition and organization, nevertheless, propagate 
themselves by simple division. In this case the whole 
organism, with all its organs, falls into two equal halves as 
soon as by growth it has attained a certain size. Each half 
again develops itself, by growth, into a complete individual. 
Here, again, it is surely self-evident that the two products 
of division will share the qualities of the parental organism, 
as they themselves are in fact halves of that parent. 

Next to propagation by division we come to propagation 
by the formation of buds. This kind of monogony is 
exceedingly widely spread. It occurs both in the case of 
simple cells (though not frequently) and in the higher organ- 


isms composed of many cells. The formation of buds is 
universal in the vegetable kingdom, less frequent in the 
animal kingdom. However, here also it occurs in the 
tribe of Plant-like Animals, especially among the Coral 
Zoophytes, and among the greater portion of the Hydroid 
Polyps very frequently, further also among some worms 
(Planarian Worms, Ring- Worms, Moss Animals, Tuni- 
cates). Most branching animal- trees or colonies, which are 
exceedingly like branching plants, arise like those plants, 
by the formation of buds. 

Propagation by the formation of buds (Gemmatio) is 
essentially distinguished from propagation by division, in 
the fact that the two organisms thus produced by budding 
are not of equal age ; and therefore at first are not of equal 
value, as they are in the case of division. In division 
we cannot clearly distinguish either of the two newly 
produced individuals as the parental, that is as the producer, 
because, in fact, both have an equal share in the composition 
of the original parental individual. If, on the other hand, 
an organism sends out a bud, then the latter is the child of 
the former. The two individuals are of unequal size and of 
unequal form. If, for instance, a cell propagates itself by 
the formation of buds, we do not see the cell fall into two 
equal halves, but there appears at one point of it a protube- 
rance, which becomes larger and larger, more or less separates 
itself from the parental cell, and then grows independently. 
In like manner we observe in the budding of a plant or 
animal, that a small local growth arises on a part of the 
mature individual, which growth becomes larger and larger, 
and likewise more or less separates itself from the parental 
organism by an independence in its growth. The bud, after 


it has attained a certain size, may either completely separate 
itself from the parental individual, or it may remain con- 
nected with it and form a stock or colony, whilst at the 
same time its life may be quite independent of that of its 
parent. While the growth which starts the propagation, in 
the case of self-division, is a total one affecting the whole 
body, it is in the formation of buds only partial, affecting 
merely a portion of the parental organism. But here, also, 
the bud — the newly-produced individual which remains so 
long most directly connected with the parental organism, 
and which proceeds from it — retains the essential qualities 
and the original tendency of development of its parent. 

A third mode of non-sexual propagation, that of the 
formation of germ-buds (Polysporogonia), is intimately 
connected with the formation of buds. In the case of the 
lower, imperfect organisms, among animals, especially in the 
case of the Plant-like animals and Worms, we very fre- 
quently find that in the interior of an individual composed 
of many cells, a small group of cells separates itself from 
those surrounding it, and that this small isolated group 
gradually developes itself into an individual, which, becomes 
like the parent, and sooner or later comes out of it. 
Thus, for example, in the body of the Fluke-worms (Tre- 
matodes) there often arise numerous little bodies consisting 
of many cells, that is germ-buds, or polyspores, which at 
an early stage separate themselves completely from the 
parent body, and leave it when they have attained a certain 
stage of development. 

The formation of germ- buds is evidently but little different 
from real budding. But, on the other hand, it is connected 
with a fourth kind of non-sexual propagation, which almost 

VOL. I. 


forms a transition to sexual reproduction, namely, the 
formation of germ-cells (Monosporogonia), which is often 
briefly called formation of spores (sporogonia). In this case 
it is no longer a group of cells, but a single cell, which 
separates itself from the surrounding cells in the interior of 
the producing organism, and which only becomes 'further 
developed after it has come out of its parent. After this 
germ-cell, or monospore (or, briefly, spore), has left the 
parental individual, it multiplies by division, and thus 
forms a many-celled organism, which by growth and 
gradual development attains the hereditary qualities of the 
parental organism. This occurs very generally among lower 
plants (Cryptogama). 

Although the formation of germ-cells very much resembles 
the formation of germ buds, it evidently and very essentially 
differs from the latter, and also from the other forms of non- 
sexual propagation which have previously been mentioned, 
by the fact that only a very small portion of the producing 
organism takes part in the propagation and, accordingly, in 
the transmission by inheritance. In the case of self -division, 
where the whole organism falls into two halves, in the 
formation of buds, where a considerable portion of the whole 
body, already more or less developed, separates from the 
producing individual, we easily understand that the forms 
and vital phenomena should be the same in the producing 
and produced organism. It is much more difficult to under- 
stand in the formation of germ-buds, and more difficult still 
in the formation of germ-cells, how this very small, quite 
undeveloped portion of the body, this group of cells, or this 
single cell, not only directly takes with it certain parental 
qualities into its independent existence, but also after its 


separation from the parental individual develops into a 
many-celled body, and in this repeats the forms and vital 
phenomena of the original producing organism. This last 
form of monogonic propagation — that of the germ cells, or 
spore-formation— leads us directly to a form of propagation 
which is the most difficult of all to explain, namely, sexual 

Sexual or amphigonic propagation (Amphigonia) is the 
usual method of propagation among all higher animals and 
plants. It is evident that it has only developed, at a very 
late period of the earth's history, from non-sexual propaga- 
tion, and apparently in the first instance from the method 
of propapation by germ-cells. In the earliest periods of the 
organic history of the earth, all organisms propagated them- 
selves in a non-sexual manner, as numerous lower organisms 
still do, especially all those which are at the lowest stage of 
organization, and which, strictly speaking, can be considered 
neither as animals nor as plants, and which therefore, as 
primary creatures, or Protista, are best excluded from both 
the animal and vegetable kingdoms. In the case of the 
higher animals and plants, the increase of individuals, as a 
rule, is at present brought about in the majority of cases by 
sexual propagation 

In all the chief forms of non-sexual propagation mentioned 
above — in fission, in the formation of buds, germ buds, and 
germ cells — the separated cell or group of cells was able by 
itself to develop into a new individual, but in the case of 
sexual propagation the cell must first be fructified by 
another generative substance. The fructifying male sperm 
must first mix with the female germ-cell (the egg) before 
the latter can develop into a new individual. These two 

196 the history of creation. 

different generative substances, the male sperm and the 
female egg, are either produced by one and the same indi- 
vidual hermaphrodite (Hermaphroditismus), or by two 
different individuals (sexual separation, Gonochorismus) 
(Gen. Morph. ii. 58, 59). 

The simpler and more ancient form of sexual propagation 
is through double-sexed individuals (Hermaphroditismus). 
It occurs in the great majority of plants, but only in a 
minority of animals, for example, in the garden snails, 
leeches, earth-worms, and many other worms. Every single 
individual among hermaphrodites produces within itself 
materials of both sexes — eggs and sperm. In most of the 
higher plants every blossom contains both the male organ 
(stamens and anther) and the female organs (style and 
germ). Every garden snail produces in one part of its 
sexual gland eggs, and in another part sperm. Many her- 
maphrodites can fructify themselves ; in others, however, 
copulation and reciprocal fructification of both hermaphro- 
dites is necessary for causing the development of the eggs. 
This latter case is evidently a transition to sexual separa- 

Sexual separation (Gonochorismus,) which characterizes 
the more complicated of the two kinds of sexual reproduc- 
tion, has evidently been developed from the condition of 
hermaphroditism at a late period of the organic history of 
the world. It is at present the universal method of propa- 
gation of the higher animals, and occurs, on the other hand, 
only in the minority of plants (for example, in many aquatic 
plants, e.g. Hydrocharis, Vallisneria ; and in trees, e.g. 
Willows, Poplars). Every organic individual, as a non- 
hermaphrodite (Gonochoristus), produces within itself only 


one of two generative substances, either the male or the 
female. The female individuals, both in animals and plants, 
produce eggs or egg-cells. The eggs of plants in the case 
of flowering plants (Phanerogama), are commonly called 
" embryo sacs " ; in the case of flowerless plants (Crypto- 
gama), " fruit spores." In animals, the male individual 
secretes the fructifying sperm (sperma) ; in plants, the 
corpuscles, which correspond to the sperm. In the Phane- 
rogama, these are the pollen grains, or flower-dust ; in the 
Cryptogama, a sperm, which, like that of most animals, 
consists of floating vibratile cells actively moving in a 
fluid — the zoosperms, spermatozoa, or sperm-cells. 

The so-called virginal reproduction (Parthenogenesis) 
offers an interesting form of transition from sexual repro- 
duction to the non-sexual formation of germ-cells (which 
most resembles it) ; it has been demonstrated to occur in 
many cases among Insects, especially by Siebold's ex- 
cellent investigations. In this case germ-cells, which 
otherwise appear and are formed exactly like egg-cells, 
become capable of developing themselves into new indi- 
viduals without requiring the fructifying seed. The most 
remarkable and most instructive of the different partheno- 
genetic phenomena are furnished by those cases in which 
the same germ-cells, according as they are fructified or not, 
produce different kinds of individuals. Among our common 
honey bees, a male individual (a drone) arises out of the 
eggs of the queen, if the egg has not been fructified ; a 
female (a queen, or working bee), if the egg has been fructi- 
fied. It is evident from this, that in reality there exists 
no wide chasm between sexual and non-sexual reproduc- 
tion, but that both modes of reproduction are directly 


connected. The parthenogenesis of Insects must probably 
be regarded as a relapse from the sexual mode of propaga- 
tion (possessed by the original parents of the insects) to the 
earlier condition of non-sexual propagation. (Gen. Morph. 
ii. 86). In any case, however, sexual reproduction, both in 
plants and animals, which seems such a wonderful process, 
has only arisen at a later date out of the more ancient 
process of non-sexual reproduction. In both cases heredity 
is a necessary part of the phenomenon. 

In all the different modes of propagation the essential 
point of the process is invariably a detachment of a portion 
of the parental organism possessing the capability of leading 
an individual, independent existence. We may, therefore, in 
all cases expect, d priori, that the produced individuals— 
which are, in fact, as is commonly said, " the flesh and 
blood " of the parents — will receive the vital characteristics 
and qualities of form which the parental individuals possess. 
It is simply a larger or smaller quantity of the parental 
material, in fact of its albuminous protoplasm, or cell- 
substance, which passes to the produced individual. But 
together with the material, its vital properties — that is, the 
molecular motions of the plasma — are transmitted, which 
then manifest themselves in its form. Inheritance by sexual 
breeding loses very much of the mysterious and wonderful 
character which it at first sight possesses for the uninitiated, 
if we consider the above-mentioned series of the different 
modes of propagation, and their connection one with another. 
It at first appears exceedingly wonderful that in the sexual 
propagation of man, and of all higher animals, the small 
egg, the minute cell, often invisible to the naked eye, is 
able to transfer to the produced organism all the qualities 


of the maternal organism, and, no less mysterious, that at 
the same time the essential qualities of the paternal 
organism are transferred to the offspring by means of the 
male sperm, which fructifies the egg-cell by means of a 
viscid substance in which minute thread-like cells or zoo- 
sperms move about. But as soon as we compare the con- 
nected stages of the different kinds of propagation, in which 
the produced organism separates itself more and more as a 
distinct growth from the parental individual, and more or 
less early enters upon its independent career; as soon as 
we consider, at the same time, that the growth and develop- 
ment of every higher organism only depends upon the 
increase of the cells composing it — that is, upon their 
simple propagation by division — it becomes quite evident 
that all these remarkable processes belong to one series. 

The life of every organic individual is nothing but a 
connected chain of very complicated material phenomena 
of motion. These motions must be considered as changes 
in the position and combination of the molecules, that is, 
of the smallest particles of animated matter (of atoms 
placed together in the most varied manner). The specific, 
definite tendency of these orderly, continuous, and inherent 
motions of life depends, in every organism, upon the 
chemical mingling of the albuminous generative matter to 
which it owes its origin. In man, as in the case of the 
higher animals which propagate themselves in a sexual 
manner, the individual vital motion commences at the 
moment in which the egg-cell is fructified by the spermatic 
filaments of the seed, in which process both generative 
substances actually mix; and here the tendency of the 
vital motion is determined by the specific, or more 


accurately, by the individual nature of the sperm as well as 
of the egg. There can be no doubt as to the purely 
mechanical material nature of this process. But here we 
stand full of wonder and astonishment before the infinite 
and inconceivable delicacy of this albuminous matter. We 
are amazed at the undeniable fact that the simple egg-cell 
of the maternal organism, and a single paternal sperm- 
thread, transfer the molecular individual vital motion of 
these two individuals to the child so accurately, that after- 
wards the minutest bodily and mental peculiarities of both 
parents reappear in it. 

Here we stand before a mechanical phenomenon of 
nature of which Virchow, whose genius founded the 
" cellular pathology," says with full justice : " If the 
naturalist cared to follow the custom of historians and 
preachers, and to clothe phenomena, which are in their way 
unique, with the hollow pomp of ponderous and sounding 
words, this would be the opportunity for him ; for we have 
now approached one of those great mysteries of animal 
nature, which encircle the region of animal life as opposed 
to all the rest of the world of phenomena. The question 
of the formation of cells, the question of the excitation of 
a continuous and equable motion, and, finally, the questions 
of the independence of the nervous system and of the soul 
— these are the great problems on which the human mind 
can measure its strength." To comprehend the relation of 
the male and female to the egg-cell is almost as much as 
to solve all those mysteries. The origin and development 
of the egg-cell in the mother's body, the transmission of 
the bodily and mental peculiarities of the father to it by 
his seed, touch upon all the questions which the human 


mind has ever raised about man's existence. And, we add, 
these most important questions are solved, by means of the 
Theory of Descent, in a purely mechanical and purely 
monistic sense ! 

There can then be no further doubt that, in the sexual 
propagation of man and all higher organisms, inheritance, 
•which is a purely mechanical process, is directly dependent 
upon the material continuity of the producing and pro- 
duced organism, just as is the case in the simplest non- 
sexual propagation of the lower organisms. However, I 
must at once take this opportunity of drawing atten- 
tion to an important difference which inheritance presents 
in sexual and non-sexual propagation. It is a fact long 
since acknowledged, that the individual peculiarities of the 
producing organism are much more accurately transmitted 
to the produced organism by non-sexual than by sexual 
propagation. Gardeners have for a long time made use of 
this fact in many ways. When, for instance, a single 
individual of a species of tree with stiff, upright branches 
accidentally produces down-hanging branches, a gardener, 
as a rule, cannot transmit this peculiarity by sexual, but 
only by non-sexual propagation. The twigs cut off such a 
weeping tree and planted as cuttings or slips, afterwards 
produce trees having likewise hanging branches, as, for 
example, the weeping willows and beeches. Seedlings, on 
the other hand, which have been reared out of the seed of 
such a weeping tree, generally have the original stiff and 
upright form of branches possessed by their ancestors. 
The same may be observed in a very striking manner in 
the so-called " copper-coloured trees," that is, varieties of 
trees which are characterized by a red or reddish brown 


colour of the leaves. Off-shoots from such copper-coloured 
trees (for example, the copper beech), which have been 
propagated by cuttings in a non-sexual manner, show the 
peculiar colour and nature of the leaves which distinguished 
the parental individual, while others reared from seeds of 
such a copper-coloured tree return to the green-coloured 
condition of leaf. 

This difference in inheritance will seem very natural when 
we consider that the material connection between the pro- 
ducing and produced individuals is much closer and lasts 
much longer in non-sexual than in sexual propagation. The 
special tendency of the molecular motion of life can there- 
fore fix itself much longer and more thoroughly in the filial 
organism, and be more strictly transmitted by non-sexual 
than by sexual propagation. All these phenomena, con- 
sidered in connection, clearly prove that the transmission of 
bodily and mental peculiarities is a purely material and 
mechanical process. By propagation a greater or lesser 
quantity of albuminous particles, and together with them the 
individual form of motion inherent in these molecules of 
protoplasm, are transmitted from the parental organism to 
the offspring. As this form of motion remains continuous, 
the more delicate peculiarities inherent in the parental 
organism must sooner or later reappear in the filial 




Distinction between Conservative and Progressive Transmission by Inherit- 
ance. — Laws of Conservative Transmission : Transmission of Inherited 
Characters. — Uninterrupted or Continuous Transmission. — Interrupted 
or Latent Transmission. — Alternation of Generations. — Kelapse. — 
Degeneracy. — Sexual Transmission.- — Secondary Sexual Characters. — 
Mixed or Amphigonous Transmission. — Hybrids. — Abridged or Simpli- 
fied Transmission. — Laws of Progressive Inheritance : Transmission of 
Acquired Characters. — Adapted or Acquired Transmission. — Fixed or 
Established Transmission. — Homochronous Transmission (Identity in 
Epoch). — Homotopic Transmission (Identity in Part) . — Adaptation and 
Mutability. — Connection between Adaptation and Nutrition. — Distinc- 
tion between Indirect and Direct Adaptation. 

In the last chapter we considered Transmission by Inherit- 
ance, one of the two universal vital activities of organisms, 
Adaptation and Inheritance, which by their interaction 
produce the different species of organisms, and we have 
endeavoured to trace this very mysterious vital activity to 
a more general physiological function of organisms, namely, 
to Propagation. This latter in its turn, like other vital 
phenomena of animals and plants, depends on physical and 
chemical relations. It is true they appear at times ex- 
ceedingly complicated, but can nevertheless in reality be 
traced to simple mechanical causes — that is, to the relations 


of attraction and repulsion in the particles or molecules — in 
fact, to the motional phenomena of matter. 

Now, before we turn our attention to the second function, 
the phenomenon of Adaptation or Mutability, which counter- 
acts the Transmission by Inheritance, it seems appropriate 
first to cast one more glance at the various manifestations of 
Heredity, which we may perhaps even now denominate the 
" laws of transmission by inheritance." Unfortunately, up 
to the present time very little has been done for this most 
important subject, either in zoology or in botany, and almost 
all we know of the different laws of inheritance is confined 
to the experiences of gardeners and farmers. It is not 
therefore to be wondered at, that on the whole these exceed- 
ingly interesting and important phenomena have not been 
investigated with desirable scientific accuracy, or reduced 
to the form of scientific laws. Accordingly, what I shall 
relate of the different laws of transmission are only some 
preliminary fragments taken out of the infinitely rich store 
which lies open to our inquiry. 

We may first divide all the different phenomena of inherit- 
ance into two groups, which we may distinguish as the 
transmission of inherited characters, and the transmission of 
acquired characters ; and we may call the former the con- 
servative transmission, and the latter the progressive trans- 
mission by inheritance. This distinction depends upon the 
exceedingly important fact that the individuals of every 
species of animals and plants can transmit to their de- 
scendants, not only those qualities which they themselves 
have inherited from their ancestors, but also the peculiar, 
individual qualities which they have acquired during their 
own life. The latter are transmitted by progressive, the 


former by conservative inheritance. We have now first to 
examine the phenomena of conservative inheritance, that is, 
the transmission of such qualities as the organism has 
already received from its parents or ancestors. (Gen. Morph. 
ii. 180.) 

Among the phenomena of conservative inheritance we are 
first struck by that which is its most general law, and which 
we may term the laiv of uninterrupted or continuous 
transmission. It is so universal among the higher animals 
and plants, that the uninitiated might overestimate its action 
and consider it as the only normal law of transmission by 
inheritance. This law simply consists in the fact that 
among most species of animals and plants, every generation 
is, on the whole, like the preceding — that the parents are as 
like the grandparents as they are like the children. " Like 
produces like," as is commonly said, but more accurately 
" similar things produce similar things." For, in reality, the 
descendants of every organism are never absolutely equal 
in all points, but only similar in a greater or less degree. 
This law is so generally known, that I need not give any 
examples of it. 

The law of interrupted or latent transmission by inherit- 
ance, which might also be termed alternating transmission, 
is in a measure opposed to the preceding law. This im- 
portant law appears principally active among many lower 
animals and plants, and manifests itself in contrast to the 
former in the fact that the offspring are not like their 
parents, but very dissimilar, and that only the third or a 
later generation becomes similar to the first. The grand- 
children are like the grandparents, but quite unlike the 
parents. This is a remarkable phenomenon, and, as is well 


known, occurs also very frequently, though in a less degree, 
in human families. Every one of my readers doubtless 
knows some members of a family who, in this or that pecu- 
liarity, much more resemble the grandfather or grandmother 
than the father or mother. Sometimes it lies in bodily 
peculiarities, for example, features of face, colour of hair, 
size of body — sometimes in mental qualities, for example, 
temperament, energy, understanding — which are trans- 
mitted in this manner. This fact may be observed in 
domestic animals as well as in the case of man. Among 
the domestic animals most liable to vary — as the dog, 
horse, and ox — breeders very frequently find that the pro- 
duct by breeding resembles the grandparents far more than 
it does its own parental organism. If we express this 
general law and the succession of generations by the letters 
of the alphabet, then A = C = E, whilst B=D=F, and 
so on. 

This very remarkable fact appears in a more striking 
way in the lower animals and plants than in the 
higher, and especially in the well-known phenomenon of 
alternation of generations (metagenesis). Here we very 
frequently find — for example, among the Planarian worms, 
sea-squirts or Tunicates, Zoophytes, and also among ferns 
and mosses — that the organic individual in the first place 
produces, by propagation, a form completely different 
from the parental form, and that only the descendants of 
this generation, again, become like the first. This regular 
change of generation was discovered by the poet Chamisso, 
on his voyage round the world in 1819, among the Salpce, 
cylindrical tunicates, transparent like glass, which float on 
the surface of the sea. Here the larger generation, the in- 


dividuals of which live isolated and possess an eye of the form 
of a horse-shoe, produce in a non-sexual manner (by the 
formation of buds) a completely different and smaller gene- 
ration. The individuals of this second smaller generation 
live united in chains and possess a cone-shaped eye. 
Every individual of such a chain produces, in a sexual man- 
ner (hermaphrodite) again, a non-sexual solitary form of the 
first and larger generation. Among the Salpse, therefore, it 
is always the first, third, and fifth generation, and in like 
manner the second, fourth, and sixth generations, that are 
entirely like one another. However, it is not always only 
one, but in other cases a number of generations, which are 
thus leapt over; so that the first generation resembles the 
fourth and seventh, the second resembles the fifth and 
eighth, the third resembles the sixth and ninth, and so on. 
Three different generations alternate with one another ; for 
example, among the neat little sea-buoys (Doliolum), small 
tunicates closely related to the Salpae. In this case it is 
A = D =G, further, B =E = H, and C = F = I. Among 
the plant-lice (Aphides), each sexual generation is followed 
by a succession of from eight to ten or twelve non-sexual 
generations, which are like one another, but differ from 
the sexual generations. Then, again, a sexual generation 
reappears like the one long before vanished. 

If we further follow this remarkable law of latent or in- 
terrupted inheritance, and take into consideration all the 
phenomena appertaining to it, we may comprise under it 
also the well-known phenomena of reversion. By the term 
" reversion " or " atavism " we understand the remarkable 
fact known to all breeders of animals, that occasionally 
single and individual animals assume a form which has not 


existed for many generations, but belongs to a generation 
which has long since disappeared. One of the most remark- 
able instances of this kind is the fact that in some horses 
there sometimes appear singular dark stripes, similar to 
those of the zebra, quagga, and other wild species of 
African horses. Domestic horses of the most different races 
and of all colours sometimes show such dark stripes ; for ex- 
ample, a stripe along the back, a stripe across the shoulders, 
and the like. The sudden appearance of these stripes can 
only be explained by the supposition that it is the effect of 
a latent transmission, a relapse into the ancient original 
form, which has long since vanished, and was once common 
to all species of horses ; the original form, undoubtedly, was 
originally striped like the zebras, quaggas, etc. In like 
manner, certain qualities in other domestic animals some- 
times appear quite suddenly, which once marked their 
wild ancestors, now long since extinct. In plants, also, such 
a relapse can be observed very frequently. All my readers 
probably know the wild yellow toad-flax (Linaria vulgaris), 
a plant very common in our fields and hedges. Its dragon- 
mouthed yellow flower contains two long and two short 
stamens. But sometimes there appears a single blossom 
(Peloria) which is funnel-shaped, and quite regularly com- 
posed of five individual and equal sections, with five corre- 
sponding stamens. This Peloria can only be explained as a 
relapse into the long since extinct and very ancient common 
form of all those plants which, like the toad-flax, possess 
dragon-mouthed, two-lipped flowers, with two long and two 
short stamens. The original form, like the Peloria, pos- 
sessed a regular five-spurred blossom, with five equal 
stamens, which only later and by degrees have become 


unequal (compare p. 17). All such relapses are to be 
brought under the law of interrupted or latent transmission, 
although the number of intervening generations may be 

When cultivated plants or domestic animals become wild, 
when they are withdrawn from the conditions of cultivated 
life, they experience- changes which appear not only as 
adaptations to their new mode of life, but partially also as 
relapses into the ancient original form out of which the cul- 
tivated forms have been developed. Thus the different 
kinds of cabbage, which are exceedingly different in form, 
may be led back to the original form, by allowing them to 
grow wild. In like manner, dogs, horses, heifers, etc., when 
growing wild, often revert more or less to a long extinct 
generation. An immensely long succession of generations 
may pass away before this power of latent transmission be- 
comes extinguished. 

A third law of conservative transmission may be called 
the law of sexual transmission, according to which each sex 
transmits to the descendants of the same sex peculiarities 
which are not inherited by the descendants of the other sex. 
The so-called secondary sexual characters, which in many 
respects are of extraordinary interest, everywhere furnish 
numerous examples of this law. Subordinate or secondary 
sexual characters are those peculiarities of one of the two 
sexes which are not directly connected with the sexual 
organs themselves ; such characters, which exclusively belong 
to the male sex, are, for example, the antlers of the stag, the 
mane of the lion, and the spur of the cock. The human 
beard, an ornament commonly denied to the female sex, be- 
longs to the same class. Similar characteristics by which 

VOL. I. p 


the female sex is alone distinguished are, for example, the 
developed breasts, with the lactatory glands of female mam- 
mals and the pouch of the female opossum. The bodily 
size, also, and complexion, differs in female animals ol many 
species from that of the male. All these secondary sexual 
qualities, like the sexual organs themselves, are transmitted 
by the male organism only to the male, not to the female, 
and vice versa. Contrary facts are rare exceptions to the 

A fourth law of transmission, which has here to be men- 
mentioned, in a certain sense contradicts the last, and limits 
it, viz. the law of mixed or mutual (amphigonous) trans- 
mission. This law tells us that every organic individual 
produced in a sexual way receives qualities from both 
parents, from the father as well as from the mother. This 
fact, that personal qualities of each of the two sexes are 
transmitted to both male and female descendants, is very 
important. Goethe mentions it of himself, in the beautiful 
lines — 

" Von Vater hab ich die Statur, des Lebens ernstes Fuhren 
Von Miitterchen die Frohnatur und Lust zu fabuliren." 

" From my father I have my stature and the serious tenour of my life, 
From my mother a joyous nature and a turn for poetizing." 

This phenomenon, I suppose, is so well-known to all, 
that I need not here enter upon it. It is according to the 
different portions of their character which father and 
mother transmit to their children, that the individual 
differences among brothers and sisters are chiefly determined. 

The very important and interesting phenomenon of hy- 
bridism also belongs to this law of mixed or amphigonous 


transmission. It alone, when rightly estimated, is quite 
sufficient to refute the prevailing dogma of the constancy 
of species. Plants, as well as animals, belonging to quite 
different species, may sexually mingle with one another 
and produce descendants which in many cases can again 
propagate themselves, and that indeed either (more fre- 
quently) by mingling with one of the two parental species, 
or (more rarely) by pure in-breeding, hybrid mixing with 
hybrid. The latter is well established, for example, in the 
hybrids of hares and rabbits (Lepus Darwinii, p. 147). The 
hybrids of a horse and a donkey, two different species of 
the same genus (Equus), are well known. These hybrids 
differ according as the father or the mother belongs to the 
one or the other species — the horse or the donkey. The 
mule produced by a mare and a he-donkey has qualities 
quite different from those of the jinny (Hinnus), the hybrid 
of a horse and she-donkey. In both cases the hybrid pro- 
duced by the crossing of two different species is a mixed 
form, which receives qualities from both parents ; but the 
qualities of the hybrid are different, according to the form 
of the crossing. In like manner, mulattoes produced by 
a European and a negress show a different mixture of 
characters from the hybrids produced by a negro with a 
European female. In these phenomena of hybrid-breed- 
ing, as well as in the other laws of transmission pre- 
viously mentioned, we are as yet unable to show the acting 
causes in detail ; but no naturalist doubts the fact that the 
causes are in all cases purely mechanical and dependent 
upon the nature of organic matter itself. If we possessed 
more delicate means of investigation than our rude organs 
of sense and auxilliary instruments, we should be able to 


discover those causes, and to trace them to the chemical and 
physical properties of matter. 

Among the phenomena of conservative transmission, we 
must now mention, as the fifth law, the law of abridged or 
simplified transmission. This law is very important in 
regard to embryology or ontogeny, that is in regard to the 
history of the development of organic individuals. Onto- 
geny, or the history of the development of individuals, as I 
have already mentioned in the first chapter (p. 10), and as I 
subsequently shall explain more minutely, is nothing but 
a short and quick repetition of Phylogeny dependent on 
the laws of transmission and adaptation — that is, a repetition 
of the palaeontological history of development of the whole 
organic tribe, or phylum, to which the organism belongs. 
If, for example, we follow the individual development of a 
man, an ape, or any other higher mammal within the ma- 
ternal body from the egg, we find that the foetus or embryo 
arising out of the egg passes through a series of very differ- 
ent forms, which on the whole agrees with, or at least runs 
parallel to, a series of forms which is presented to us by the 
historical chain of ancestors of the higher mammals. Among 
these ancestors we may mention certain fishes, amphibians, 
marsupials, etc. But the parallelism or agreement of these 
two series of development is never quite complete ; on the 
contrary, in ontogeny there are always gaps and leaps which 
indicate the omission of certain stages belonging to the 
phylogeny. Fritz Miiller, in his excellent work, " Fur 
Darwin," 16 has clearly shown in the case of the Crus- 
tacea, or crabs, that " the historical record preserved in the 
individual history of development is gradually obscured, 
in proportion as development takes a more and more direct 


route from the egg to the complete animal." This process 
of obscuring and shortening is determined by the law of 
abridged transmission, and I mention it here specially be- 
cause it is of great importance for the understanding of 
embryology, and because it explains the fact, at first so 
strange, that the whole series of forms which our ancestors 
have passed through in their gradual development are no 
longer visible in the series of forms of our own individual 
development from the egg. 

Opposed to the laws of the conservative transmission, 
hitherto discussed, are the phenomena of the transmission of 
the second series, that is, the laws of progressive transmis- 
sion by inheritance. As already mentioned, they depend 
upon the fact that the organism transmits to its descendants 
not only those qualities which it has inherited from its own 
ancestors, but also a number of those individual qualities 
which it has acquired during its own lifetime. Adaptation 
is here seen to be connected with transmission by inherit- 
ance (Gen Morph. ii. 186). 

At the head of these important phenomena of progressive 
transmission, we may mention the law of adapted or ac- 
quired transmission. In reality it asserts nothing more 
than what I have said above, that in certain circumstances 
the organism is capable of transmitting to its descendants 
all the qualities which it has acquired during its own life 
by adaptation. This phenomenon, of course, shows itself 
most distinctly when the newly acquired peculiarity pro- 
duces any considerable change in the inherited form. This 
is the case in the examples I mentioned in the preceding 
chapter as to transmission in general, in the case of the men 
with six fingers and toes, the porcupine men, copper beeches, 


weeping willows, etc. The transmission of acquired diseases, 
such as consumption, madness, and albinism, likewise form 
very striking examples. Albinoes are those individuals who 
are distinguished by the absence of colouring matter, or 
pigments, in the skin. They are of frequent occurrence 
among men, animals, and plants. In the case of animals of 
a definite dark colour, individuals are not unfrequently born 
which are entirely without colour, and in animals possessing 
eyes, this absence of pigment extends even to the eyes, so 
that the iris of the eye, which is commonly of a bright or 
intense colour, is colourless, but appears red, on account of 
the blood-vessels being seen through it. Among many 
animals, such as rabbits and mice, albinoes with white fur 
and red eyes are so much liked that they are propagated in 
great numbers as a special race. This would be impossible 
were it not for the law of the transmission of adaptations. 

Which of the changes acquired by an organism are trans- 
mitted to its descendants, and which are not, cannot be 
determined a priori, and we are unfortunately not ac- 
quainted with the definite conditions under which the 
transmission takes place. We only know in a general way 
that certain acquired qualities are much more easily trans- 
mitted than others, for example, more easily than the 
mutilations caused by accidents. These latter are generally 
not transmitted by inheritance, otherwise the descendants of 
men who have lost their arms or legs would be born without 
the corresponding arm or leg ; but here, also, exceptions 
occur, and a race of dogs without tails has been produced 
by consistently cutting off the tails of both sexes of the dog 
during several generations. A few years ago a case occurred 
on an estate near Jena, in which by a careless slamming of 


a stable door the tail of a bull was wrenched off, and the 
calves begotten by this bull were all born without a tail. 
This is certainly an exception ; but it is very important to 
note the fact, that under certain unknown conditions such 
violent changes are transmitted in the same manner as 
many diseases. 

In very many cases the change which is transmitted and 
preserved by adapted transmission is constitutional or in- 
born, as in the case of albinism mentioned before. The 
change then depends upon that form of adaptation which 
we call the indirect or potential. A very striking instance 
is furnished by the hornless cattle of Paraguay, in South 
America. A special race of oxen is there bred which is 
entirely without horns. It is descended from a single bull, 
which was born in 1770 of an ordinary pair of parents, and 
the absence of horns was the result of some unknown cause. 
All the descendants of this bull produced with a horned cow 
were entirely without horns. This quality was found 
advantageous, and by propagating the hornless cattle among 
one another, a hornless race was obtained, which at present 
has almost entirely supplanted the horned cattle in Paraguay. 
The case of the otter-sheep of North America forms a similar 
example. In the year 1791 a farmer, by name Seth Wright, 
lived in Massachusetts, in North America ; in his normally 
formed flock of sheep a lamb was suddenly born with a sur- 
prisingly long body and very short and crooked legs. It 
was therefore unable to take any great leaps, and especially 
unable to leap across a hedge into a neighbour's garden 
— a quality which seemed advantageous to the owner, as the 
territories were divided by hedges. It therefore occurred to 
him to transmit this quality to other sheep, and by crossing 


this ram with normally shaped ewes, he produced a whole 
race of sheep, all of which had the qualities of the father, 
short and crooked legs and a long body. None of them 
could leap across the hedges, and they therefore were much 
liked and propagated in Massachusetts. 

A second law, which likewise belongs to the series of 
progressive transmissions, may be called the law of estab- 
lished or habitual transTYiission. It manifests itself in this, 
that qualities acquired by an organism during its individual 
life are the more certainly transmitted to its descendants 
the longer the causes of that change have been in action, 
and that this change becomes the more certainly the pro- 
perty of all subsequent generations the longer the cause of 
change acts upon these latter also. The quality newly 
acquired by adaptation or mutation must be established 
or constituted to a certain degree before we can cal- 
culate with any probability that it will be transmitted 
at all to the descendants. In this respect transmission re- 
sembles adaptation. The longer a newly acquired quality 
has been transmitted by inheritance, the more certainly 
will it be preserved in future generations. If, therefore, 
for example, a gardener by methodical treatment has pro- 
duced a new kind of apple, he may calculate with the 
greater certainty upon preserving the desired peculiarity 
of this sort the longer he has transmitted the same by 
inheritance. The same is clearly shown in the trans- 
mission of diseases. The longer consumption or madness 
has been hereditary in a family the deeper is the root of 
the evil, and the more probable it is that all succeeding 
generations will suffer from it. 

We may conclude the consideration of the phenomena of 


inheritance with the two very important laws of homotopic 
and contemporaneous transmission by inheritance. We 
understand by them the fact that changes acquired by an 
organism during its life, and transmitted to its descendants, 
appear in the same part of the body in which the parental 
organism was first affected by them, and that they also 
appear in the offspring at the same age as that at which 
they did so in the parent. 

The law of contemporaneous or homochronous transmis- 
sion, which Darwin calls the law of " transmission in 
corresponding periods of life," can be shown very clearly 
in the transmission of diseases, especially of such as are 
recognized as very destructive, on account of their here- 
ditary character. They generally appear in the organism 
of the child at the time corresponding with that in which 
the parental organism contracted the disease. Hereditary 
diseases of the lungs, liver, teeth, brain, skin, etc., usually 
appear in the descendants at the same period, or a little 
earlier than they showed themselves in the parental organ- 
ism, or were contracted by it. The calf gets its horns at 
the same period of life as its parents did. In like manner 
the young stag receives its antlers at the same period of life 
in which they appeared in its father or grandfather. In 
every one of the different sorts of vine the grapes ripen at 
the same time as they did in the case of their progenitors. 
It is well known that the time of ripening varies greatly in 
the different sorts ; but as all are descended from a single 
species, this variation has been acquired by the progenitors 
of the several sorts, and has then been transmitted by 

The law of homotopic transmission, which is most 


closely connected with the last mentioned law, and which 
might be called the law of transmission in corresponding 
parts of the body, may also be very distinctly recognized in 
pathological cases of inheritance. Large moles, for example, 
or accumulations of pigment in several parts of the skin, 
tumours also, often appear during many generations, not only 
at the same period of life, but also in the same part of the 
skin. Excessive development of fat in certain parts of the 
body is likewise transmitted by inheritance. Above all, it 
is to be noted that numerous examples of this, as well as of 
the preceding law, may be found everywhere in the study of 
embryology. Both the law of homochronous and liomotopic 
transmission are fundamental lavjs of embryology, or 
ontogeny. For these laws explain the remarkable fact that 
the different successive forms of individual development in 
all generations of one and the same species always appear 
in the same order of succession, and that the variations of the 
body always take place in the same parts. This apparently 
simple and self-evident phenomenon is nevertheless exceed- 
ingly wonderful and curious; we cannot explain its real 
causes, but may confidently assert that they are due to the 
direct transmission of the organic matter from the parental 
organism to that of the offspring, as we have seen above in 
the case of the process of transmission in general, by a con- 
sideration of the details of the various modes of reproduction. 
Having thus, then, considered the most important laws of 
Inheritance, we now turn to the second series of phenomena 
bearing on natural selection, viz. to those of Adaptation or 
Variation. These phenomena, taken as a whole, stand in a 
certain opposition to the phenomena of Inheritance, and the 
difficulty which arises in examining them consists mainly 


in the two sets of phenomena being so completely inter- 
crossed and interwoven. We are but seldom able to say 
with certainty — of the variations of form which occur before 
our eyes — how much is owing to Inheritance, and how much 
to Adaptation. All characters of form, by which organisms 
are] distinguished, are caused either by Inheritance or by 
Adaptation ; but as both functions are continually inter- 
acting with each other, it is extremely difficult for the 
systematic inquirer to recognize the share belonging to each 
of the two functions in the special structure of individual 
forms. This is, at present, all the more difficult, because we 
are as yet scarcely aware of the immense importance of this 
fact, and because most naturalists have neglected the theory 
of Adaptation, as well as that of Inheritance. The laws of 
Inheritance, which we have just discussed, as well as the 
laws of Adaptation, which we shall consider directly, in 
reality form only a small portion of the phenomena existing 
in this domain, but which have not as yet been investi- 
gated ; and since every one of these laws can interact with 
every other, it is clear that there is an i nfini te complication 
of physiological actions, which are at work in the con- 
struction of organisms. 

But now, as to the phenomenon of variation or adaptation 
in general, we must, as in the case of inheritance, view it as 
a quite universal, physiological fundamental quality of all 
organisms, without exception — as a manifestation of life 
which cannot be separated from the idea of organism. 
Strictly speaking, we must here also, as in the case of in- 
heritance, distinguish between Adaptation itself and Adapta- 
bility. By Adaptation (Adaptio), or Variation (Variatio), we 
understand the fact that the organism, in consequence of 


influences of the surrounding outer -world, assumes certain 
new peculiarities in its vital activity, composition, and form 
which it has not inherited from its parents ; these acquired 
individual qualities are opposed to those which have been 
inherited, or, in other words, those which have been trans- 
mitted to it from its parents or ancestors. On the other 
hand, we call Adaptability (Adaptabilitas), or Variability 
(Variabilitas), the capability inherent in all organisms to 
acquire such new qualities under the influence of the outer 
world. (Gen. Morph. ii. 191.) 

The undeniable fact of organic adaptation or variation is 
universally known, and can be observed at every moment in 
thousands of phenomena surrounding us. But just because 
the phenomena of variation by external influences appear so 
self-evident, they have hitherto undergone scarcely any 
accurate scientific investigation. To them belong all the 
phenomena which we look upon as the results of contracting 
and giving up habits, of practice and giving up practices, or 
as the results of training, of education, of acclimatization, of 
gymnastics, etc. Many permanent variations brought about 
by causes producing disease, that is to say, many diseases, 
are nothing but dangerous adaptations of the organism to 
injurious conditions of life. In the case of cultivated plants 
and domestic animals, variation is so striking and powerful 
that the breeder of animals and the gardener found their 
whole mode of proceeding upon it, or rather upon the inter- 
action between these phenomena and those of Inheritance. 
It is also well known to every one that animals and plants, 
in their wild state, are subject to variation. Every syste- 
matic treatise on a group of animals or plants, if it were to 
be quite complete and exhaustive, ought to mention in every 


individual species the number of variations which differ 
more or less from the prevailing or typical form of the 
species. Indeed, in every careful systematic special treatise 
one finds, in the case of most species, mention of a number of 
such variations, which are described sometimes as individual 
deviations, and sometimes as so-called races, varieties, de- 
generate species, or subordinate species, and which often 
differ exceedingly from the original species, solely in con- 
sequence of the adaptation of the organism to the external 
conditions of life. 

If we now endeavour to fathom the general causes of these 
phenomena of Adaptation, we arrive at the conclusion that 
in reality they are as simple as the causes of the phenomena 
of Inheritance. We have shown that the nature of the 
process of propagation furnishes the real explanation of 
the facts of Transmission by Inheritance, that is, the trans- 
mission of parental matter to the body of the offspring; 
and in like manner we can show that the physiological 
function of nutrition, or change of substance, affords a 
general explanation of Adaptation or Variation. When I 
here point to "nutrition" as the fundamental cause of 
variation and adaptation, I take this word in its widest sense, 
and I understand by it the whole of the material changes 
which the organism undergoes in all its parts through the 
influences of the surrounding outer world. Nutrition thus 
comprises not only the reception of actual nutritive sub- 
stances and the influence of different kinds of food, but 
also, for example, the action upon the organism of water 
and of the atmosphere, the influence of sunlight, of tem- 
perature, and of all those meteorological phenomena which 
are implied in the term "climate." The indirect and 


direct influence of the nature of the soil and of the 
dwelling-place also belong to it ; and further, the extremely 
important and varied influence which is exercised upon 
every animal and every plant by the surrounding organ- 
isms, friends and neighbours, enemies and robbers, para- 
sites, etc. All these and many other very important 
influences, all of which more or less modify tbe organism in 
its material composition, must be taken into consideration 
in studying the change of substance which goes on in living 
things. Adaptation, accordingly, is the consequence of all 
those material variations which are produced in the change 
of substance of the organism by the external conditions of 
existence, or by the influences of the surrounding external 

How very much every organism is dependent upon the 
whole of its external surroundings, and changed by their 
alteration, is, in a general way, well known to every one. 
Only think how much the human power of action is de- 
pendent upon the temperature of the air, or how much the 
disposition of our minds depends upon the colour of the sky. 
Accordingly as the sky is cloudless and sunny, or covered 
with large heavy clouds, our state of mind is cheerful or dull. 
How differently do we feel and think in a forest during a 
stormy winter night and during a bright summer day ! 
All the different moods of our soul depend upon purely 
material changes of our brain, upon movements of molecular 
plasma, which are started through the medium of the senses 
by the different influences of light, warmth, moisture, etc. 
" We are a plaything to every pressure of the air." No less 
important and deeply influential are the effects produced 
upon our mind and body by the different quality and 


quantity of food. Our mental activity, the activity of our 
understanding and of our imagination, is quite different 
accordingly as we have taken tea or coffee, wine or beer, 
before or during our work. Our moods, wishes, and feelings 
are quite different when we are hungry and when we are 
satisfied. The national character of Englishmen and 
Gauchos, in South America, who live principally on meat 
and food rich in nitrogen, is wholly different from that of 
the Irish, feeding on potatoes, and that of the Chinese, living 
on rice, both of whom take food deficient in nitrogen. The 
latter also form much more fat than the former. Here, as 
everywhere, the variations of the mind go hand in hand 
with the corresponding transformations of the body ; both 
are produced by purely material causes. But all other 
organisms, in the same way as man, are varied and changed 
by the different influences of nutrition. It is well known 
that we can change in an arbitrary way the form, size, 
colour, etc., of our cultivated plants and domestic animals, 
by change of food ; that, for example, we can take from 
or give to a plant definite qualities, accordingly as we 
expose it to a greater or less degree of sunlight and moisture. 
As these phenomena are generally widely known, and as we 
shall proceed presently to the consideration of the different 
laws of adaptation, we will not dwell here any longer on 
the general facts of variation. 

As the different laws of transmission may be naturally 
divided into the two series of conservative and progressive 
transmission, so we may also distinguish between two series 
of the laws of adaptation, first, the series of laws of indirect, 
and secondly, the series of laws of direct adaptation. The 
latter may also be called the laws of actual, and the former 
the laws of potential, adaptation. 


The first series, comprising the phenomena of indirect 
(potential) adaptation, has, on the whole, hitherto been 
little attended to, and Darwin has the merit of having 
directed special attention to this series of changes. It is some- 
what d iffi cult to place this subject clearly before the reader ; 
I will endeavour to make it clear hereafter by examples. 
Speaking quite generally, indirect or potential adaptation 
consists in the fact that certain changes in the organism, 
effected by the influence of nutrition (in its widest sense) and 
of the external conditions of existence in general, show them- 
selves not in the individual form of the respective organism, 
but in that of its descendants. Thus, especially in organisms 
propagating themselves in a sexual way, the reproductive 
system, or sexual apparatus, is often influenced by external 
causes (which little affect the rest of the organism), to such a 
degree that its descendants show a complete alteration of 
form. This can be seen very strikingly in artificially pro- 
duced monstrosities. Monstrosities can be produced by sub- 
jecting the parental organism to certain extraordinary con- 
ditions of life, and, curiously enough, such an extraordinary 
condition of life does not produce a change of the organ- 
ism itself, but a change in its descendants. This cannot be 
called transmission by inheritance, because it is not a quality 
existing in the parental organism that is transmitted by 
inheritance. It is, on the contrary, a change affecting the 
parental organism, but not perceptible in it, that appears in 
the peculiar formation of its descendants. It is only the 
impulse to this new formation which is transmitted in pro- 
pagation through the egg of the mother or the sperm of 
the father. The new formation exists in the parental 
organism only as a possibility (potential) ; in the descend- 
ants it becomes a reality (actual). 


As this very important and very general phenomenon had 
hitherto heen entirely neglected, people were inclined to 
consider all the visible variations and transformations of 
organic forms as phenomena of adaptation of the second 
series, that is, as phenomena of direct or actual adaptation. 
The essence of this latter kind of adaptation consists in the 
fact that the change affecting the organism (through nutri- 
tion, etc.) shows itself immediately by some transformation, 
and does not only make itself apparent in the descend- 
ants. To this class belong all the well-known phenomena 
in which we can directly trace the transforming influence of 
climate, food, education, training, etc., in their effects upon 
the individual itself. 

"We have seen how the two series of phenomena of pro- 
gressive and conservative transmission, in spite of their 
difference in principle, in many ways interfere with and 
modify each other, and in many ways co-operate with and 
cross each other. The same is the case, in a still higher 
degree, in the two series of phenomena of indirect and 
direct adaptation, which are opposed to each other and yet 
closely connected. Some naturalists, especially Darwin and 
Carl Vogt, ascribe to the indirect or potential adaptation 
by far the more important and almost exclusive influence. 
But the majority of naturalists have hitherto been inclined 
to take the opposite view, and to attribute the principal 
influence to direct or actual adaptation. I consider this 
controversy, in the mean while, as almost useless. It is but 
seldom that we are in a condition, in any individual case of 
variation, to judge how much of it belongs to direct and 
how much to indirect adaptation. We are, on the whole, 
still too little acquainted with these exceedingly important 

VOL. I. Q 


and intricate relations, and can only assert, in a general 
way, that the transformation of organic forms is to be 
ascribed either to direct adaptation alone, or to indirect 
adaptation alone, or lastly, to the co-operation of both direct 
and indirect adaptation. 

( 227 ) 



Laws of Indirect or Potential Adaptation. — Individual Adaptation. — 
Monstrous or Sudden Adaptation. — Sexual Adaptation. — Laws of Direct 
or Actual Adaptation. — Universal Adaptation. — Cumulative Adaptation. 
— Cumulative Influence of External Conditions of Existence and 
Cumulative Counter-Influence of the Organism. — Free Will.— Use and 
Non-use of Organs. — Practice and Habit. — Correlative Adaptation. — 
Correlation of Development. — Correlation of Organs. — Explanation of 
Indirect or Potential Adaptation by the Correlation of the Sexual 
Organs and of the other parts of the Body. — Divergent Adaptation. — 
Unlimited or Infinite Adaptation. 

In the last chapter we reduced into two groups the phe- 
nomena of Adaptation or Variation, which, in connection 
and interaction with the phenomena of Heredity, produce 
all the endless variety of forms in animals and plants — 
first, the group of indirect or potential, and secondly, the 
group of direct or actual Adaptation. We shall occupy 
ourselves with a closer examination of the different laws 
which we can discover in these two groups of the phe- 
nomena of variation. Let us first take into consideration 
the remarkable and very important, although hitherto 
much neglected, phenomena of indirect variation. 

Indirect or potential adaptation manifests itself, it will be 
remembered, in the striking and exceedingly important fact 


that organic individuals experience transformations and 
assume forms in consequence of changes of nutrition which 
have not operated on them themselves, hut upon their 
parental organism. The transforming influence of the 
external conditions of existence, of climate, of nutrition, 
etc., shows its effects here not directly in the transform- 
ation of the organism itself, but indirectly in that of its 
descendants. (Gen. Morph. ii. 202.) 

As the principal and most universal of the laws of in- 
direct variation must be mentioned the law of indi- 
vidual adaptation, or the important proposition that all 
organic individuals from the commencement of their indi- 
vidual existence are unequal, although often very much 
alike. As a proof of this proposition, I may at once point 
to the fact, that in the human race in general all brothers 
and sisters, all children of the same parents, are unequal 
from their birth. No one will venture to assert that two 
children at their birth are perfectly alike : that the size of 
the individual parts of their bodies, the number of hairs on 
their heads, the number of cells composing their outer skins 
or epidermis, the number of blood-cells are the same in both 
children, or that both children have come into the world 
with the same abilities or talents. But what more specially 
proves this law of individual difference, is the fact that in 
the case of those animals which produce several young ones 
at a time, — for instance, dogs and cats, — all the young of 
each birth differ from one another more or less strikingly 
in size and colour of the individual parts of the body, or 
in strength, etc. Now this law is universal. All organic 
individuals from their beginning are distinguished by cer- 
tain, though often extremely minute, differences, and the 


cause of these individual differences, though in detail usually 
utterly unknown to us, depends partly or entirely on certain 
influences which the organs of propagation in the parental 
organism have undergone. 

A second law of indirect adaptation, which we shall 
call the law of monstrous or sudden adaptation, is of less 
importance and less general than the law of individual 
adaptation. Here the divergences of the child-organism 
from the parental form are so striking that, as a rule, we 
may designate them as monstrosities. In many cases they 
are produced, as has been proved by experiments, by the 
parental organism having been subject to a certain treat- 
ment, and placed under peculiar conditions of nutrition ; for 
example, when air and light are withdrawn from it, or when 
other influences powerfully acting upon its nutrition are 
changed in a certain way. The new condition of existence 
causes a strong and striking modification of form, not 
directly of the organism itself, but only of that of its de- 
scendants. The mode of this influence in detail we cannot 
discover, and we can only in a very general way detect a 
causal connection between the abnormal formation of the 
child and a certain change in the conditions of existence 
of its parents exerting a special influence upon the organs 
of propagation in the latter. The previously mentioned 
phenomenon of albinism probably belongs to this group of 
abnormal or sudden variations, also the individual cases 
of human beings with six fingers and toes, the case of 
the hornless cattle, as well as those of sheep and goats 
with four or six horns. The abnormal deviation in all 
these cases probably owes its origin to a cause which 
at first only affected the reproductive system of the 


parental organism, the egg of the mother or the sperm of 
the father. 

A third curious manifestation of indirect adaptation may- 
he termed the law of sexual adaptation. Under this name 
we indicate the remarkahle fact that certain influences, 
which act upon the male organs of propagation only, affect 
the structure of the male descendants, and in like manner 
other influences, which act upon the female organs of propa- 
gation only, manifest their effect only in the change of struc- 
ture of the female descendants. This remarkable pheno- 
menon is still very obscure, and has not as yet been 
investigated, but is probably of great importance in regard 
to the origin of " secondary sexual characteristics," to which 
we have already made allusion. 

All the phenomena of sexual, monstrous, and individual 
adaptation, which we may comprise under the name of the 
laws of indirect or potential adaptation, are as yet very 
little known to us in their real nature and in their deeper 
causal connection. Only this much we can at present main- 
tain with certainty, that numerous and important trans- 
formations in organic forms owe their existence to this 
process. Many and striking variations of form solely de- 
pend on causes which at first only affect the nutrition of the 
parental organism, and specially its organs of propagation. 
Evidently the relations in which the sexual organs stand to 
other parts of the body are of the greatest importance. We 
shall have more to say of these presently, when we speak of 
the law of correlative adaptation. How powerfully the 
variations in the conditions of life and nutrition affect the 
propagation of organisms is rendered obvious by the re- 
markable fact that numerous wild animals which we keep 


in our zoological gardens, and exotic plants which are grown 
in our botanical gardens, are no longer able to reproduce 
themselves. This is the case, for example, with most birds of 
prey, parrots, and monkeys. The elephant, also, and the 
animals of prey of the bear genus, in captivity hardly ever 
produce young ones. In like manner many plants in a cul- 
tivated state become sterile. The two sexes may indeed 
unite, but no fructification, or no development of the fructi- 
fied germ, takes place. From this it follows with certainty 
that the changed mode of nutrition in the cultivated state is 
able completely to destroy the capability of reproduction, 
and therefore to exercise the greatest influence upon the 
sexual organs. In like manner other adaptations or varia- 
tions of nutrition in the parental organism may cause, not 
indeed a complete want of descendants, but still important 
changes in their form. 

Much better known than the phenomena of indirect or 
potential adaptation are those of direct or actual adapta- 
tion, to the consideration of which we now turn our at- 
tention. To them belong all those changes of organisms 
which are generally considered to be the results of practice, 
habit, training, education, etc. ; also those changes of or- 
ganic forms which are effected directly by the influence of 
nutrition, of climate, and other external conditions of exist- 
ence. As has already been remarked in direct or actual 
adaptation, the transforming influence of the external cause 
affects the form of the organism itself, and does not only 
manifest itself in that of the descendants. (Gen. Morph. 
ii. 207.) 

We may place the law of universal adaptation at the 
head of the different laws of direct or actual adaptation, 


because it is the chief and most comprehensive among them. 
It may be briefly explained in the following proposition : 
" All organic individuals become unequal to one another in 
the course of their life by adaptation to different conditions 
of life, although the individuals of one and the same species 
remain mostly very much alike." A certain inequality of 
organic individuals, as we have seen, was already to be 
assumed in virtue of the law of individual (indirect) adapt- 
ation But, beyond this, the original inequality of indivi- 
duals is afterwards increased by the fact that every individual, 
during its own independent life, subjects and adapts itself 
to its own peculiar conditions of existence. All different 
individuals of every species, however like they may be in 
their first stages of life, become in the further course of 
their existence less like to one another. They deviate 
from one another in more or less important peculiari- 
ties, and this is a natural consequence of the different condi- 
tions under which the individuals live. There are no two 
single individuals of any species which can complete their 
life under exactly the same external circumstances. The 
vital conditions of nutrition, of moisture, air, light ; further, 
the vital conditions of society, the inter-relations with 
surrounding individuals of the same or other species, are 
different in every individual being ; and this difference 
first affects the functions, and later changes the form of 
every individual organism. If the children of a human 
family show, even at the beginning, certain individual 
inequalities which we may consider as the consequence 
of individual (indirect) adaptation, they will appear 
still more different at a later period of life, when each 
child has passed through different experiences, and has 


adapted itself to different conditions of life. The original 
difference of the individual processes of development, evi- 
dently becomes greater the longer the life lasts and the 
more various the external conditions which influence the 
separate individuals. This may be demonstrated in the 
simplest manner in man, as well as in domestic animals and 
cultivated plants, in which the vital conditions may be ar- 
bitrarily modified. Two brothers, of whom one is brought 
up as a workman and the other as a priest, develop quite 
differently in body as well as in mind ; in like manner, two 
dogs of one and the same birth, of which one is trained as a 
sporting dog and the other chained up as a watch dog. The 
same observation may also readily be made as to organic in- 
dividuals in a natural state. If, for instance, one carefully 
compares all the trees in a fir or beech forest, which con- 
sists of trees of a single species, one finds that among 
all the hundreds or thousands of trees, there are not two 
individual trees completely agreeing in size of trunk and 
other parts, in the number of branches, leaves, etc. Every- 
where we find individual inequalities which, in part at 
least, are merely the consequences of the different conditions 
of life under which the trees have developed. It is true we 
can never say with certainty how much of this dissimilarity 
in all the individuals of every species may have originally 
been caused by indirect individual adaptation, and how 
much of it acquired under the influence of direct or uni- 
versal adaptation. 

A second series of phenomena of direct adaptation, which 
we may comprise under the law of cumulative adaptation, 
is no less important and general than universal adaptation. 
Under this name I include a great number of very important 


phenomena, which are usually divided into two quite 
distinct groups. Naturalists, as a rule, have distinguished, 
first, those variations of organisms which are produced 
directly by the permanent influence of external conditions 
(by the constant action of nutrition, of climate, of suiTound- 
ings, etc.), and secondly, those variations which arise from 
habit and practice, from accustoming themselves to definite 
conditions of life, and from the use and non-use of organs. 
The latter influences have been set forth especially by 
Lamarck as important causes of the change of organic 
forms, while the former have for a very long time been 
recognized as such more generally. 

The sharp distinction usually made between these two 
groups of cumulative adaptation, and which even Darwin 
still maintains, disappears as soon as we reflect more 
accurately and deeply upon the real nature and causal 
foundation of these two, apparently very different, series 
of adaptations. We then arrive at the conviction that in 
both cases there are always two different active causes to 
be dealt with : on the one hand the external influence or 
action of adaptative conditions of life, and on the other 
hand the internal reaction of the organism which subjects 
and adapts itself to that condition of life. If cumulative 
adaptation is considered from the first point of view alone, 
and the transforming actions of the permanent external con- 
ditions of life are traced to those conditions solely, then the 
principal stress is laid unduly upon the external factor, and 
the necessary internal reaction of the organism is not taken 
into proper consideration. If, on the other hand, cumulative 
adaptation is unjustly regarded solely in relation to its 
second factor, and the transforming action of the organism 


itself, its reaction against the external influences, its change 
by practice, habit, use, or non-use of organs, is put into the 
foreground, then we forget that this reaction is first called 
into play by the action of external conditions of existence. 
Hence it seems that the distinction made between these two 
groups lies only in the different manner of viewing them, 
and I believe that they can, with full justice, be considered 
as one. The most essential fact in these phenomena of 
cumulative adaptation is that the change of the organism 
which manifests itself first in the functions, and at a later 
period in the form, is the result either of long enduring, or 
of often repeated, influences of an external cause. The 
smallest cause, by cumulation of its action, can attain the 
greatest results. 

There are innumerable examples of this kind of direct 
adaptation. In whatever direction we may examine the 
life of animals and plants, we discover on all hands 
evident and undeniable changes of this kind. Let me first 
mention some of those phenomena of adaptation occasioned 
directly by nutrition itself. Every one knows that the 
domestic animals which are bred for certain purposes can 
be variously modified, according to the different quantity 
and quality of the food given to them. If a farmer in 
breeding sheep wishes to produce fine wool, he gives them 
different food from what he would give if he wished to obtain 
good flesh or an abundance of fat. Choice race and 
carriage horses receive better food than dray and cart 
horses. Even the bodily form of man — for example, the 
amount of fat — is quite different according to his nutrition. 
Food containing much nitrogen produces little fat, that 
containing little nitrogen produces a great deal of fat. 


People who, by means of Banting's system, at present so 
popular, wish to become thin eat only meat and eggs — no 
bread, no potatoes. The important variations that can be 
produced among cultivated plants, solely by changing the 
quantity and quality of nourishment, are well known. The 
same plant acquires an altogether different appearance, 
according as it is placed in a dry and warm place, exposed 
to the sunlight or placed in a cool damp spot in the shade. 
Many plants, if transferred to the sea shore, get in a short 
space of time thick, fleshy leaves, and the same plants 
placed in a particularly dry and hot locality get thin hairy 
leaves. All these variations arise directly from the cumu- 
lative influence of changed nutrition. 

But it is not only the quantity and quality of the articles 
of nutrition which affect and powerfully change and trans- 
form the organism, but it is affected also by all the other 
external conditions of existence, above all by its nearest 
organic surroundings, the society of friendly or hostile 
organisms. One and the same kind of tree develops itself 
quite differently in an open locality, where it is free on 
all sides, and in a forest where it must adapt itself to its 
surroundings, where it is pressed on all sides by its 
nearest neighbours, and is forced to shoot upwards. In 
the former case, the branches of the tree spread widely out ; 
in the latter, the trunk extends upwards, and the top of 
the tree remains small and contracted How powerfully 
all these circumstances, and how powerfully the hostile or 
friendly influence of surrounding organisms, of parasites, 
etc., affect every animal and every plant, is so well known, 
that it appears superfluous to quote further examples. The 
change of form, or transformation which is thereby effected, 


is never solely the direct result of the external influence, 
but must always be traced to the corresponding reaction, 
and to the activity of the organism itself, which consists in 
contracting a habit, or practice, and in the use or non-use of 
organs. The fact that these latter phenomena, as a rule, 
have been considered distinct from the former, is owing first 
to the one-sided manner of viewing them already mentioned, 
and secondly to the wrong notion which has been formed 
as to the nature and the influence of the activity of the 
will in animals. 

The activity of the will, which is the organ of habit, of 
practice, of the use or non-use of organs among animals, is, 
like every other activity of the animal soul, dependent upon 
material processes in the central nervous system, upon 
peculiar motions which emanate from the albuminous 
matter of the ganglion cells, and the nervous fibres con- 
nected with them. The will, as well as the other mental 
activities, in higher animals, in this respect is different from 
that of men only in quantity, not in quality. The will of 
the animal, as well as that of man, is never free. The 
widely spread dogma of the freedom of the will is, from a 
scientific point of view, altogether untenable. Every 
physiologist who scientifically investigates the activity of 
the will in man and animals, must of necessity arrive at the 
conviction that in reality the will is never free, but is 
always determined by external or internal influences. These 
influences are for the most part ideas which have been 
either formed by Adaptation or by Inheritance, and are 
traceable to one or other of these two physiological functions. 
As soon as we strictly examine the action of our own will; 
without the traditional prejudice about its freedom, we 


perceive that every apparently free action of the will is 
the result of previous ideas, which are based on notions 
inherited or otherwise acquired, and are therefore, in the 
end, dependent on the laws of Adaptation and Inheritance. 
The same also applies to the action of the will in all animals. 
As soon as their will is considered in connection with their 
mode of life, in its relation to the changes which the mode 
of life is subject to from external conditions, we are at once 
convinced that no other view is possible. Hence the changes 
of the will which follow the changes of nutrition, and 
which, in the form of practice, habit, etc., produce variations 
in structure, must be reckoned among the other material 
processes of cumulative adaptation. 

Whilst an animal's will is adapting itself to changed 
conditions of existence by the acquisition of new habits, 
practices, etc., it not unfrequently effects the most remark- 
able transformations of the organic form. Numerous 
instances of this may be found everywhere in animal life. 
Thus, for example, many organs iu domestic animals are 
suppressed, when in consequence of a changed mode of life 
they cease to act. Ducks and fowls in a wild state fly 
exceedingly well, but lose this facility more or less in a 
cultivated state. They accustom themselves to use their 
legs more than their wings, and in consequence the muscles 
and skeleton used in flying are essentially changed in their 
development and form. Darwin has proved this by a very 
careful comparative measurement and weighing of the 
respective parts of the skeleton in the different races of 
domestic ducks, which are all descended from the wild duck 
(Anas boschas). The bones of the wings in tame ducks are 
weaker, the bones of the legs, on the other hand, are more 


strongly developed than in wild ducks. In ostriches and 
other running birds which have become completely unac- 
customed to fly, the consequence is that their wings are 
entirely crippled and degenerate into mere " rudimentary 
organs" (p. 12). In many domestic animals, especially in 
many races of dogs and rabbits, we find that in the 
cultivated state they have acquired pendulous ears. This 
is simply a consequence of a diminished use of the auri- 
cular muscles. In a wild state these animals have to exert 
their ears very much in order to discover an approaching 
foe, and this is accompanied by a strong development of 
the muscular apparatus, which keeps the outer ears in an 
upright position, and by which they can turn them in all 
directions. In a domestic state the same animals no longer 
require to listen so attentively, they prick up or turn their 
ears only a little ; the auricular muscles cease to be used, 
gradually become weakened, and the ears hang down 
flabbily, or become rudimentary. 

As in these cases the function, and consequently the form 
also, of the organ becomes degenerated through disuse, so, 
on the other hand, it becomes more developed by greater 
use. This is particularly striking if we compare the brain, 
and the mental activity belonging to it, in wild animals 
and those domestic animals which are descended from 
them. The dog and horse, which are so vastly improved 
by cultivation, show an extraordinary degree of mental 
development, in comparison with their wild original 
ancestors, and evidently the change in the bulk of the 
brain, which is connected with it, is mainly determined by 
persistent exercise. It is also well known how quickly 
and powerfully muscles grow and change their form by con- 


tinual practice. Compare, for example, the arms and legs 
of a trained gymnast with those of an immovable book- 

How powerfully external influences affect the habits of 
animals and their mode of life, and in this way still further 
change their forms, is very strikingly shown ,in many cases 
among amphibious animals and reptiles. Our commonest 
indigenous snake, the ringed snake, lays eggs which require 
three weeks' time to develop. But when it is kept in 
captivity, and no sand is strewn in the cage, it does not lay 
its eggs, but retains them until the young ones are developed. 
The difference between animals producing living offspring 
and those laying eggs is here effaced simply by the change 
of the ground upon which the animal lives. 

The water-salamanders, or tritons, which have been 
artificially made to retain their original gills, are extremely 
interesting in this respect. The tritons are amphibious 
animals, nearly akin to frogs, and possess, like the latter, 
in their youth external organs of respiration — gills — with 
which they, while living in water, breathe the air dissolved 
in the water. At a later date a metamorphosis takes place 
in tritons, as in frogs. They leave the water, lose their gills, 
and accustom themselves to breathe with their lungs. But 
if they are prevented from doing this by being kept shut up 
in a tank, they do not lose their gills. The gills remain, and 
the water salamander continues through life in that low 
sta^e of development, beyond which its lower relations, the 
gilled salamanders, or Sozobranchiata, never pass. The gilled 
salamander attains its full size, its sexual development, and 
reproduces itself without losing its gills. 

Great interest was caused a short time ago, among 


zoologists, by the axolotel (Siredon pisciformis), a gilled 
salamander from Mexico, nearly related to the triton ; it 
had already been known for a long time, and been bred on a 
large scale in the zoological garden in Paris. This animal 
possesses external gills, like the young salamander, but 
retains them all its life, like all other Sozobranchiata. This 
gilled salamander generally remains in the water, with its 
aquatic organs of respiration, and also propagates itself 
there. But in the Paris garden, unexpectedly from among 
hundreds of these animals, a small number crept out of 
the water on to the dry land, lost their gills, and changed 
themselves into gill-less salamanders, which are not to be 
distinguished from a North-American genus of tritons 
(Amblystoma), and breathe only through lungs. In this 
exceedingly curious case we can directly follow the great 
stride from water-breathing to air-breathing animals, a 
stride which can indeed be observed every spring in the 
individual history of development of frogs and salamanders. 
Just as every separate frog and every separate salamander 
transforms itself from an amphibious animal breathing 
through gills, at a later period into one breathing through 
lungs, so the whole group of frogs and salamanders have 
arisen from animals breathing through gills, and akin to the 
Siredon. The Sozobranchiata have remained up to the 
present day in that low stage of development. Ontogeny 
here explains phylogeny ; the history of the development 
of individuals explains that of the whole group (p. 10). 

To the law of accumulative adaptation there closely fol- 
lows a third law of direct or actual adaptation, the law of 
correlative adaptation. According to this important law, 
actual adaptation not only changes those parts of the 

vol. I. R 


organism which are directly affected by its influence, but 
other parts also not directly affected by it. This is the 
consequence of organic solidarity, and especially of the 
unity of the nutrition existing among all the parts of 
every organism. If, for example, the hairiness of the leaves 
increases in a plant by its being transferred to a dry locality, 
then this change reacts upon the nutrition of other parts, 
and it may result in a shortening of the parts of the stalk, 
and produce a more contracted form of the whole plant. 
In some races of pigs and dogs— for example, in the 
Turkish dog — which by adaptation to a warmer climate have 
more or less lost their hair, the teeth also have degenerated. 
Whales and Endentata (armadillos), which by their curious 
skin-covering are removed from the other mammals, also 
show the greatest deviations in the formation of their teeth. 
Further, those races of domestic animals (oxen and pigs) 
which have acquired short legs have, as a rule, also a short 
and compact head. Among other examples, the races of 
pigeons which have the longest legs are also characterized by 
the longest beaks. The same correlation between the length 
of the legs and beaks is universal in the order of stilted-birds 
(Grallatores), in storks, cranes, snipe, etc. The correlations 
which thus exist between different parts of the organism 
are most remarkable, but their real cause is unknown to us. 
In general, we can of course say, the changes of nutrition 
affecting an individual part must necessarily react on the 
other parts, because the nutrition of every organism is a 
connected, centralized activity. But why just this or that 
part should exhibit this or that particular correlation is in 
most cases quite unknown to us. We know a great number 
of such correlations in nutrition ; they are especially seen in 


those changes of animals and plants which give rise to an 
absence of pigment (noticed previously) — in albinoes. The 
want of the usual colouring matter goes hand in hand with 
certain changes in the formation of other parts ; for example, 
of the muscular and osseous system, consequently of organic 
systems which are not at all ultimately connected with 
the system of the outer skin. Yery frequently albinoes are 
more feebly developed, and consequently the whole structure 
of the body is more delicate and weak than in coloured 
animals of the same species. The organs of the senses and 
nervous system are in like manner curiously affected when 
there is this want of pigment. White cats with blue eyes 
are nearly always deaf. White horses are distinguished 
from coloured horses by their special liability to form sarko- 
matous tumours. In man, also, the degree of the development 
of pigment in the outer skin greatly influences the suscepti- 
bility of the organism for certain diseases ; so that, for 
instance, Europeans with a dark complexion, black hair, 
and brown eyes become more easily acclimatized to tropical 
countries, and are less subject to the diseases there prevalent 
(inflammation of the liver, yellow fever, etc.) than Europeans 
of white complexion, fair hair, and blue eyes. (Compare 
above, p. 150.) 

Among these correlations in the formation of different 
organs, those are specially remarkable which exist between 
the sexual organs and other parts of the body. No change 
of any part reacts so powerfully upon the other parts of the 
body as a certain treatment of the sexual organs. Farmers 
who wish to obtain an abundant formation of fat in pigs 
sheep, etc., remove the sexual organs by cutting them out 
(castration), and this is indeed done to animals of both sexes, 


The result is an excessive development of fat. The same is 
done to the singers in certain religious corporations. These 
unfortunates are castrated in early youth, in order that they 
may retain their high boyish voices. In consequence of this 
mutilation of the genitals, the larynx remains in its youth- 
ful stage of development. The muscular tissues of the body 
remain at the same time weakly developed, while below the 
skin an abundance of fat accumulates. But this mutilation 
also powerfully reacts upon the development of the nervous 
system, the energy of the will, etc., and it is well known that 
human castrates, or eunuchs, as well as castrated animals, are 
utterly deficient in the special psychical character which 
distinguishes the male sex. Man is a man, both in body 
and soul, solely through his male generative glands. 

These most important and influential correlations between 
the sexual organs and the other parts of the body, especially 
the brain, are found equally in both sexes. This might be 
expected even a priori, because in most animals the two 
kinds of organs develop themselves from the same foun- 
dation, and at the beginning are not different. In man, as 
in the rest of the vertebrate animals, the male and female 
organs in the original state of the germ are entirely the 
same, and the differences of the two sexes only gradually 
arise in the course of embryonic development (in man, in the 
ninth week of embryonic life), by one and the same gland 
developing in the female as the ovary, and in the male as 
the testicle. Every change of the female ovary, therefore, 
has a no less important reaction upon the whole female 
organism than every change of the testicle has upon the male 
organism. Virchow has expressed the importance of this 
correlation in his admirable essay on " Das Weib und die 


Zelle " (" Woman and the Cell "), in the following words : — 
" Woman is woman only by her sexual glands ; all the 
peculiarities of her body and mind, of her nutrition and her 
nervous activity, the sweet delicacy and roundness of her 
limbs, the peculiar formation of the pelvis, the develop- 
ment of the breasts, the continuance of the high voice, that 
beautiful ornament of hair on her head, with the scarcely 
perceptible soft down on the rest of the skin — then again, 
the depth of feeling, the truth of her direct perceptions, her 
gentleness, devotion, and fidelity — in short, all the feminine 
qualities which we admire and honour in a true woman are 
but a dependence of the ovary. Take this ovary away, and 
the man- woman stands before us — a loathly abortion." 

The same close correlation between the sexual organs and 
the other parts of the body occurs among plants as generally 
as among animals. If one wishes to obtain an abundance of 
fruit from a garden plant, the growth of the leaves is cur- 
tailed by cutting off some of them. If, on the other hand, 
an ornamental plant with a luxuriance of large and beautiful 
leaves is desired, then the development of the blossoms and 
fruit is prevented by cutting off the flower buds. In both 
cases one system of organs develops at the cost of the others. 
Thus, also, most variations in the formation of leaves in 
wild plants result in corresponding transformations of the 
generative parts or blossoms. The great importance of this 
" compensation of development," of this " correlation of 
parts," has been already set forth by Goethe, by Geoffroy St. 
Hilaire, and other nature-philosophers. It rests mainly 
upon the fact that direct or actual adaptation cannot pro- 
duce an important change in a single part of the body, 
without at the same time affecting the whole organism. 


The correlative adaptation between the reproductive organs 
and the other parts of the body deserves a very special con- 
sideration, because it is, above all others, likely to throw 
light upon the obscure and mysterious phenomena of in- 
direct or potential adaptation, which have already been 
considered. For just as every change of the sexual organs 
powerfully reacts upon the rest of the body, so on the other 
hand every important change in another part of the body 
must necessarily more or less react on the sexual organs. 
This reaction, however, will only become perceptible in the 
formation of the offspring which arise out of the changed 
generative parts. It is, in fact, precisely those remarkable 
and imperceptible changes of the genital system (in them- 
selves utterly insignificant changes) — changes of the eggs 
and the sperm — brought about by such correlations, which 
have the greatest influence upon the formation of the off- 
spring, and all the phenomena of indirect or potential adapt- 
ation previously mentioned may in the end be traced to 
correlative adaptation. 

A further series of remarkable examples of correlative 
adaptation is furnisbed by the different animals and plants 
which become degenerated through parasitic life or para- 
sitism. No other change in the mode of life so much 
affects the shapes of organisms as the adoption of a 
parasitical life. Plants thereby lose their green leaves ; as, 
for instance, our native parasitical plants, Orobanche, La- 
thraea, Monotropa. Animals which originally have lived 
freely and independently, but afterwards adopt a parasitical 
mode of life on other animals or plants, in the first place 
cease to use their organs of motion and their organs of 
sense. The loss of this activity is succeeded by the loss of 


the organs themselves, and thus we find, for example, many 
crabs, or Crustacea, which in their youth possess a tolerably 
high degree of organization, viz. legs, antennae, and eyes, in 
old age completely degenerate, living as parasites, with- 
out eyes, without apparatus of motion, and without antennae. 
The lively, active form of youth, has become a shapeless, 
motionless lump. Only the most necessary organs of nutri- 
tion and propagation retain their activity ; all the rest of 
the body has degenerated. Evidently these complete trans- 
formations are, to a large extent, the direct consequences of 
cumulative adaption, of the non-use and defective exercise 
of the organs, but a great portion of them must certainly 
be attributed also to correlative adaptation. (Compare Plate 
X. and XL). 

A seventh law of adaptation, the fourth in the group of 
direct adaptation, is the law of divergent adaptation. By 
this law we indicate the fact that parts originally formed 
alike have developed in different ways under the influence 
of external conditions. This law of adaptation is extremely 
important for the explanation of the phenomenon of 
division of labour, or polymorphism. We can see this 
very easily in our own selves ; for instance, in the activity 
of our two hands. We usually accustom our right hand 
to quite different work from that which we give our left, 
and in consequence of the different occupation there arises 
a different formation of the two hands. The right hand, 
which we use much more than the left, shows a stronger 
development of the nerves, muscles, and bones. The same 
applies to the whole arm. In most human beings the 
bones and flesh of the right arm are, in consequence 
of their being more employed, stronger and heavier than 


those of the left arm. Now, as the special use of the right 
arm has been adopted and transmitted by inheritance for 
thousands of years among Europeans, the stronger shape 
and size of the right arm have already become hereditary. 
P. Harting, an excellent Dutch naturalist, has shown by 
measuring and weighing newly-born children, that even in 
them the right arm is more developed than the left. 

According to the same law of divergent adaptation, both 
eyes also frequently develop differently. If, for example, a 
naturalist accustoms himself always to use one eye for the 
microscope (it is better to use the left), then that eye will 
acquire a power different from that of the other, and this 
division of labour is of great advantage. The one eye will 
become more short-sighted, and better suited for seeing 
things near at hand ; the other eye becomes, on the contrary, 
more long-sighted, more acute for looking at an object in the 
distance. If, on the other hand, the naturalist alternately uses 
both eyes for the microscope, he will not acquire the short- 
sightedness of the one eye and the compensatory degree of 
long-sight in the other, which is attained by a wise distribu- 
tion of these different functions of sight between the two 
eyes. Here then again the function, that is the activity, of 
originally equally -formed organs can become divergent by 
habit ; the function reacts again upon the form of the organ, 
and thus we find, after a long duration of such an influence, 
a change in the more delicate parts and the relative growth 
of the divergent organs, which in the end becomes apparent 
even in their coarser outlines. 

Divergent adaptation can very easily be perceived among 
plants, especially in creepers. Branches of one and the 
same creeping plant, which originally were formed alike, 


acquire a completely different form and extent, a completely 
different degree of curvature and diameter of spiral winding, 
according as they twine themselves round a thinner or a 
thicker bar. The divergent change of form of parts origin- 
ally identical in form, which tending in different directions 
develop themselves under different external conditions, can 
be distinctly demonstrated in many other examples. As 
this divergent adaptation interacts with progressive inherit- 
ance, it becomes the cause of a division of labour among the 
different organs. 

An eighth and last law of adaptation we may call the 
law of unlimited or infinite adaptation. By it we simply 
mean to express that we know of no limit to the variation 
of organic forms occasioned by the external conditions of 
existence. We can assert of no single part of an organism, 
that it is no longer variable, or that if it were subjected to 
new external conditions it would not be changed by them. 
It has never yet been proved by experience that there is a 
limit to variation. If, for example, an organ degenerates 
from non-use, this degeneration ends finally in a complete 
disappearance of the organ, as is the case with the eyes of 
many animals. On the other hand, we are able, by continual 
practice, habit, and the ever-increasing use of an organ, to 
bring it to a degree of perfection which we should at 
the beginning have considered to be impossible. If we com- 
pare the uncivilized savages with civilized nations, we find 
among the former a development of the organs of sense — 
sight, smell, and hearing — such as civilized nations can 
hardly conceive of. On the other hand, the brain, that is 
mental activity, among more civilized nations is developed 
to a degree of which the wild savages have no idea. 


There appears indeed to be a limit given to the adapt- 
ability of every organism, by the " type " of its tribe or 
phylum ; that is, by the essential fundamental qualities 
of this tribe, which have been inherited from a common 
ancestor, and transmitted by conservative inheritance to all 
its descendants. Thus, for example, no vertebrate animal 
can acquire the ventral nerve-chord of articulate animals, 
instead of the characteristic spinal marrow of the vertebrate 
animals. However, within this hereditary primary form, 
within this inalienable type, the degree of adaptability is 
unlimited. The elasticity and fluidity of the organic 
form manifests itself, within the type, freely in all directions, 
and to an unlimited extent. But there are some animals, 
as, for example, the parasitically degenerate crabs and 
worms, which seem to pass even the limit of type, and 
have forfeited all the essential characteristics of their tribe 
by an astonishing degree of degeneration. As to the 
adaptability of man, it is, as in all other animals, also un- 
limited, and since it is manifested in him above all other 
animals, in the modifications of the brain, there can be 
absolutely no limit to the knowledge which man in a 
further progress of mental cultivation may not be able to 
exceed The human mind, according to the law of unlimited 
adaptation, enjoys an infinite perspective of becoming ever 
more and more perfect. 

These remarks are sufficient to show the extent of the 
phenomena of Adaptation, and the great importance to 
be attached to them. The laws of Adaptation, or the 
facts of Variation caused by the influence of external con- 
ditions, are just as important as the laws of Inheritance. 
All phenomena of Adaptation, in the end, can be traced to 


conditions of nutrition of the organism, in the same way 
as the phenomena of Inheritance are referable to conditions 
of reproduction ; but the latter, as well as the former, 
may further be traced to chemical and physical, that is to 
mechanical, causes. According to Darwin's Theory of 
Selection the new forms of organisms, the transformations 
which artificial selection produces in the state of cultivation, 
and which natural selection produces in the state of nature, 
arise solely by the interaction of such causes. 

( 2 52 ) 



Interaction of the Two Organic Formative Causes, Inheritance and Adapta- 
tion. — Natural and Artificial Selection. — Struggle for Existence, or 
Competition for the Necessaries of Life. — Disproportion between the 
Number of Possible or Potential, and the Number of Eeal or Actual 
Individuals. — Complicated Correlations of all Neighbouring Organisms. 
— Mode of Action in Natural Selection. — Homochromic Selection as the 
Cause of Sympathetic Colourings. — Sexual Selection as the Cause of the 
Secondary Sexual Characters. — Law of Separation or Division of 
Labour (Polymorphism, Differentiation, Divergence of Characters). — 
Transition of "Varieties into Species. — Idea of Species. — Hybridism. — 
Law of Progress or Perfectioning (Progressus, Teleosis). 

In order to arrive at a right understanding of Darwinism, 
it is, above all, necessary that the two organic functions 
of Inheritance and Adaptation, which we spoke of in 
our last chapter, should be more closely examined. If we 
do not, on the one hand, examine the purely mechanical 
nature of these two physiological activities, and the various 
action of their different laws, and if, on the other hand, we 
do not consider how complicated the interaction of these 
different laws of Inheritance and Adaptation must be, we 
shall not be able to understand how these two functions, by 
themselves, have been able to produce all the variety of 


animal and vegetable forms, -which, in fact, they have. We 
have, at least, hitherto been unable to discover any other 
formative causes besides these two, and if we rightly under- 
stand the necessary and infinitely complicated interaction 
of Inheritance and Adaptation, we do not require to look 
for other unknown causes for the change of organic forms. 
These two fundamental causes are, as far as we can see, 
completely sufficient. 

Even long before Darwin had published his Theory of 
Selection, some naturalists, and especially Goethe, had as- 
sumed the interaction of two distinct formative tendencies 
— a conservative or preserving, and a progressive or chang- 
ing formative tendency — as the causes of the variety of 
organic forms. The former was called by Goethe the cen- 
tripetal or specifying tendency, the latter the centrifugal 
tendency, or the tendency to metamorphosis (p. 89). These 
two tendencies completely correspond with the two processes 
of Inheritance and Adaptation. Inheritance is the centri- 
petal or internal formative tendency which strives to keep 
the organic form in its species, to form the descendants like 
the parents, and always to produce identical things from 
generation to generation. Adaptation, on the other hand, 
which counteracts inheritance, is the centrifugal or external 
formative tendency, which constantly strives to change the 
organic forms through the influence of the varying agencies 
of the outer world, to create new forms out of those existing, 
and entirely to destroy the constancy or permanency of 
species. Accordingly as Inheritance or Adaptation pre- 
dominates in the struggle, the specific form either remains 
constant or changes into a new species. The degree of con- 
stancy of form in the different species of animals and 


plants, which obtains at any moment, is simply the 
necessary result of the momentary predominance which 
either of these two formative powers (or physiological 
activities) has acquired over the other. 

If we now return to the consideration of the process of 
selection or choice, the outlines of which we have already 
examined, we shall be in a position to see clearly and dis- 
tinctly that both artificial and natural selection rest solely 
upon the interaction of these two formative tendencies. If 
we. carefully watch the proceedings of an artificial selector — 
a farmer or a gardener — we find that only these two con- 
structive forces are used by him for the production of new 
forms. The whole art of artificial selection rests solely upon 
a thoughtful and wise application of the laws of Inheritance 
and Adaptation, and upon their being applied and regulated 
in an artistic and systematic manner. Here the will of man 
constitutes the selecting force. 

The case of natural selection is quite similar, for it also 
employs merely these two organic constructive forces, these 
ingrained physiological properties of Adaptation and Here- 
dity, in order to produce the different species. But the 
selecting principle or force, which in artificial selection is 
represented by the conscious will of man acting for a definite 
purpose, consists in natural selection of the unconscious 
struggle for existence acting without a definite plan. "What 
we mean by " struggle for existence " has already been ex- 
plained in the seventh chapter. It is the recognition of 
this exceedingly important identity which constitutes one 
of the greatest of Darwin's merits. But as this relation is 
very frequently imperfectly or falsely understood, it is 
necessary to examine it now more closely, and to illustrate 


by a few examples the operation of the struggle for life, and 
the operation of natural selection by means of the struggle 
for life (Gen. Morph. ii. 231). 

When considering the struggle for life, we started from 
the fact that the number of germs which all animals and 
plants produce is infini tely greater than the number of 
individuals which actually come to life and remain alive 
for a longer or shorter time. Most organisms produce 
during life thousands or millions of germs, from each of 
which, under favourable circumstances, a new individual 
might arise. In most animals and plants these germs are 
eggs, that is cells, which for their development require 
sexual fructification. But among the Protista, the lowest 
organisms, which are neither animals nor plants, and which 
propagate themselves only in a non-sexual manner, the germ- 
cells, or spores, require no fructification. Now, in all cases 
the number of unsexual, as well as of sexual germs, is out 
of all proportion to the number of actually living indi- 
viduals of every species. 

Taken as a whole, the number of living animals and plants 
on our earth remains always about the same. The number 
of places in the economy of nature is limited, and in most 
parts of the earth's surface these places are always approxi- 
mately occupied. Certainly there occur everywhere and in 
every year fluctuations in the absolute and in the relative 
number of individuals of all species. However, taken as a 
whole, these fluctuations are of little importance, and it is 
broadly the fact that the total number of all individuals 
remains, on an average, almost constant. There is a 
constant fluctuation, which depends on the fact that in one 
year or another one or other series of animals and plants 


predominates, and that every year the struggle for life some- 
what alters their relations. 

Every single species of animals aod plants would have 
densely peopled the whole earth's surface in a short time, if 
it had not had to struggle against a number of enemies and 
hostile influences. Even Linnaeus calculated that if an 
annual plant only produced two seeds (and there is not one 
which produces so few), it would have yielded in twenty 
years a million of individuals. Darwin has calculated of 
elephants, which of all animals seem the slowest to increase, 
that in seven hundred and fifty years the descendants of a 
single pair would amount to nineteen millions of indi- 
viduals ; this is supposing that every elephant, during its 
period of fertility (from the 30th to the 90th year), pro- 
duced only three pairs of young ones, and survived itself 
to its hundredth year. In like manner the increase 
of the number of human beings — if calculated on the 
average proportion of births to population, and no hin- 
drances to the natural increase stood in the way — would be 
such as to double the total in twenty-five years. In every 
century the total number of men would have increased six- 
teen-fold ; whereas we know that the total number of 
human beings increases but slowly, and that the increase of 
population is very different in different countries. While 
European tribes spread over the whole globe, other tribes or 
species of men every year draw nearer to their complete 
extinction. This is the case especially with the redskins of 
America, and with the copper-coloured natives of Australia. 
Even if these races were to propagate more abundantly than 
the white Europeans, yet they would sooner or later succumb 
to the latter in the struggle for life. But of all human 


individuals, as of all other organisms, by far the majority 
perish at the earliest period of their lives. Of the im- 
mense quantity of germs which every species produce, only 
very few actually succeed in developing, and of these few 
it is again only a very small portion which attain to the age 
in which they can reproduce themselves (compare p. 161). 

From the disproportion between the immense excess of 
organic germs and the small number of chosen individuals 
which are actually able to continue in existence beside one 
another, there follows of necessity that universal struggle 
for life, that constant fight for existence, that perpetual com- 
petition for the necessaries of life, of which I gave a 
sketch in my seventh chapter. It is this struggle for life 
which brings natural selection into play, which in its 
turn is made use of by the interaction of the phenomena of 
Inheritance and Adaptation as a sifting agency, and which 
thus causes a continual change in all organic forms. In 
this struggle for acquiring the necessary conditions of 
existence, those individuals will always overpower their 
rivals who possess any individual privilege, any advan- 
tageous quality, of which their fellow competitors are 
destitute. It is true we are able only in the fewest 
cases (in those animals and plants best known to us) to 
form an approximate conception of the infinitely com- 
plicated interaction of the numerous circumstances, all 
of which here come into combination. Only think how 
infinitely varied and complicated are the relations of 
every single human being to the rest of mankind, and in 
general, to the whole of the surrounding outer world. But 
similar relations prevail also among all animals and plants 
which live together in one place. All influence one another 

vol. 1. S 


actively or passively. Every animal and every plant 
struggles directly with a number of enemies, beasts of prey, 
parasitic animals, etc. Plants standing together struggle 
with one another for the space of ground requisite for their 
roots, for the necessary amount of light, air, moisture, etc. 
In like-manner, animals living together struggle with one 
another for their food, dwelling-place, etc. In this most 
active and complicated struggle, any personal superiority, 
however small, any individual advantage, may possibly 
decide the issue in favour of the one possessing it. This 
privileged individual remains the victor in the struggle, and 
propagates itself, while its fellow-competitors perish before 
they succeed in propagating themselves. The personal ad- 
vantage which gave it the victory is transmitted by inherit- 
ance to its descendants, and by a further development may 
become so strongly marked as to cause us to consider the 
later generations as a new species. 

The infinitely complicated correlations which exist be- 
tween the organisms of every district, and which must be 
looked upon as the real conditions of the struggle for 
life, are mostly unknown to us, and are very difficult 
to discover. We have hitherto been able to trace them 
only to a certain point in individual cases, as in the 
example given by Darwin of the relations between cats and 
red clover in England. The red clover (Trifolium pratense), 
which in England is among the best fodder for cattle, 
requires the visit of humming-bees in order to attain the 
formation of seeds. These insects, while sucking the honey 
from the bottom of the flower, bring the pollen in contact 
with the stigma, and thus cause the fructification of the 
flower, which never takes place without it. Darwin has 


shown by experiments, that red clover which is not visited 
by humming-bees does not yield a single seed. The number 
of bees is determined by the number of their enemies, the 
most destructive of which are the field-mice. The more the 
field-mice predominate, the less the clover is fructified. The 
number of field-mice, again, is dependent upon the number 
of their enemies, principally cats. Hence in the neighbour- 
hood of villages and towns, where many cats are kept, there 
are plenty of bees. A great number of cats, therefore, is 
evidently of great advantage for the fructification of clover. 
This example may be followed still further, as has been done 
by Carl Vogt, if we consider that cattle which feed on red 
clover are one of the most important foundations of the 
wealth of England. Englishmen preserve their bodily and 
mental powers chiefly by making excellent meat — roast beef 
and beefsteak — their principal food. The English owe the 
superiority of their brains and minds over those of other 
nations in a great measure to their excellent meat. But this 
is clearly indirectly dependent upon the cats, which pursue 
the mice. We may, with Huxley, even trace the chain of 
causes to those old maids who cherish and keep cats, and, 
consequently, are of the greatest importance to the fructifi- 
cation of the clover and to the prosperity of England. From 
this example we can see that the further it is traced the 
wider is the circle of action and of correlation. We can 
with certainty maintain that there exist a great number of 
such correlations in every plant and in every animal, only 
we are not always able to point out and survey their con- 
catenation as in the last instance. 

Another remarkable example of important correlations is 
the following, given by Darwin. In Paraguay, there are 

I. H- 


no wild oxen and horses, as in the neighbouring parts of 
South America, both north and south of Paraguay. This 
surprising circumstance is explained simply by the fact that 
in that country a kind of small fly is very frequent, and is 
in the habit of laying its eggs in the navel of newly-born 
calves and foals. The newly-born animals die in conse- 
quence of this attack, and the small deadly fly is therefore 
the cause of oxen and horses never becoming wild in that 
district. Supposing that this fly were destroyed by some 
insect-eating bird, then these large mammals would grow 
wild in Paraguay, as well as in the neighbouring parts of 
South America ; and as they would eat a quantity of certain 
species of plants, the whole flora, and, consequently again, 
the whole fauna of the country would become changed It 
is hardly necessary to state, that at the same time the whole 
economy, and consequently the character, of the human 
population would alter. 

Thus the prosperity, nay, even the existence of whole 
populations can be indirectly determined by a single small 
animal or vegetable form in itself extremely insignificant. 
There are small coral islands whose human inhabitants live 
almost entirely upon the fruit of a species of palm. The 
fructification of this palm is principally effected by insects, 
which carry the pollen from the male to the female palm 
trees. The existence of these useful insects is endangered 
by insect-eating bh'ds, which in their turn are pursued by 
birds of prey. The birds of prey, however, often succumb 
to the attack of a small parasitical mite, which develops itself 
in miUions in their feathers. This small, dangerous parasite, 
again, may be killed by parasitical moulds. Moulds, birds 
of prey, and insects would in this case favour the prosperity 


of the palm, and consequently of man ; birds, mites, and 
insect-eating birds would, on the other hand, endanger it. 

Interesting examples in relation to the change of correla- 
tions in the struggle for life are furnished also by those 
isolated oceanic islands, uninhabited by man, on which at 
different times goats and pigs have been placed by 
navigators. These animals become wild, and having no 
enemies, they increase in number so excessively, that the 
rest of the animal and vegetable population suffer in conse- 
quence, and the island finally may become almost a waste, 
because there is insufficient food for the large mammals 
which increase too numerously. In some cases on an island 
thus overrun with goats and pigs, other navigators have let 
loose a couple of dogs, who enjoyed this superabundance of 
food, and they again increased so numerously, and made 
such havoc among the herds, that after several years the dogs 
themselves lacked food, and they also almost died out. The 
equilibrium of species continually changes in this manner in 
nature's economy, accordingly as one or another species 
increases at the expense of the rest. In most cases the 
relations of different species of animals and plants to one 
another are much too complicated for us to be able to follow 
them, and I leave it to the reader to picture to himself what 
an infinitely complicated machinery is at work in every part 
of the world in consequence of this struggle. The impulses 
which started the struggle, and which altered and modified 
it in different places, are in the end seen to be the impulses 
of self-preservation — in fact, the instinct leading individuals 
to preserve themselves (the instinct of obtaining food), and 
the instinct leading them to preserve the species (instinct of 
propagation). It is these two fundamental instincts of 


organic self-preservation of which Schiller, the idealist (not 
Goethe, the realist ! ) says : 

" Meanwhile, until philosophy 
Sustains the structure of the world, 
Her workings will be carried on 
By hunger and by love."* 

It is these two powerful fundamental instincts which, by 
their varying activity, produce such extraordinary differ- 
ences in species through the struggle for life. They are 
the foundations of the phenomena of Inheritance and 
Adaptation. We have, in fact, traced all phenomena of 
Inheritance to propagation, all phenomena of Adaptation to 
nutrition, as the two wider classes of material phenomena 
to which they belong. 

The struggle for life in natural selection acts with as 
much selective power as does the will of man in artificial 
selection. The latter, however, acts according to a plan and 
consciously, the former without a plan and unconsciously. 
This important difference between artificial and natural 
selection deserves especial consideration. For we learn by 
it to understand how arrangements serving a purpose 
can be produced by mechanical causes acting without an 
object, as well as by causes acting for an object. The 
products of natural selection are arranged even more for a 
purpose than the artificial products of man, and yet they 
owe their existence not to a creative power acting for a 
definite purpose, but to a mechanical relation acting uncon- 

* " Einstweilen bis den Bau der Welt 
Philosophie zusammenhalt, 
Erhalt sich ihr Getriebe 
Durcb. Hunger und durch Liebe. 


sciously and without a plan. If we had not thoroughly 
considered the interaction of Inheritance and Adaptation 
under the influence of the struggle for life, we should not 
at first he inclined to expect such results from this natural 
process of selection as are, in fact, furnished by it. It may 
therefore be appropriate here to mention a few especially 
striking examples of the activity of natural selection. 

Let us first take Darwin's homochromic selection of 
animals, or the so-called " sympathetic selection of colours," 
into consideration. Earlier naturalists have remarked that 
numerous animals are of nearly the same colour as their 
dwelling-place, or the surroundings in which they per- 
manently live. Thus, for example, plant-lice and many 
other insects living on leaves are of a green colour. The 
inhabitants of the deserts, the jerboa, or leaping mice, foxes 
of the desert, gazelles, lions, etc., are mostly of a yellow or 
yellowish-brown colour, like the sand of the desert. The 
polar animals, which live on the ice and snow, are white or 
grey, like ice and snow. Many of these animals change their 
colour in summer and winter. In summer, when the snow 
partly vanishes, the fur of these polar creatures becomes 
brownish-grey or blackish, like the naked earth, while in 
winter it again becomes white. Butterflies and insects 
which hover round the gay and bright flowers are like them 
in colour. Now, Darwin explains this surprising circum- 
stance quite simply by the fact that such colours as agree 
with the colour of the habitation are of the greatest use to 
the animals concerned. If these animals are animals of 
prey, they will be able to approach the object of their 
pursuit more safely and with less likelihood of observation, 
and, in like manner, those animals which are pursued will 


be able to escape more easily, if their colour is as little 
different as possible from that of their surroundings. If 
therefore originally an animal species varied so as to present 
cases of all colours, those individuals whose colour most 
resembled the surroundings must have been most favoured 
in the struggle for life. They remained more unobserved, 
maintained and propagated themselves, while those 
individuals or varieties differently coloured died out. 

I have tried to explain, by the same sympathetic selection 
of colour, the wonderful fact that the majority of pelagic 
animals — that is, of those which live on the surface of the 
open sea — are bluish, or completely colourless and trans- 
parent, like glass and water itself. Such colourless, glassy 
animals are met with in the most different classes. To them 
belong, among fish, the Helmicthyidse, through whose 
crystalline bodies the words of a book can be read ; among 
the molluscs, the finned snails (Heteropods) and sea- butter- 
flies, or whales-food (Pteropods) ; among worms, the Salpse, 
Alciope, and Sagitta ; further, a great number of pelagic 
crabs (Crustacea), and the greater part of the Medusae 
Umbrella-jellies, (Discomedusse) ; Comb-jellies, (Ctenophora). 
All of these pelagic animals, which float on the surface of 
the ocean, are transparent and colourless, like glass and like 
the water itself, while their nearest kin live at the bottom of 
the ocean, and are coloured and opaque like the inhabitants 
of the land. This remarkable fact, like the sympathetic 
colouring of the inhabitants of the earth, can be ex- 
plained by natural selection. Among the ancestors of the 
pelagic glass-like animals which showed a different degree of 
colourlessness and transparency, those that were the most 
colourless and transparent must have been most favoured 


in the active struggle for life which takes place on the 
surface of the ocean. They were enabled to approach their 
prey the most easily unobserved, and were themselves least 
observed by their enemies. Hence they could preserve and 
propagate themselves more easily than their more coloured 
and opaque relatives ; and finally, by accumulative adaptation 
and transmission by inheritance, through natural selection, 
in the course of many generations their bodies would attain 
that degree of crystal-like transparency and colourlessness 
which we at present aclmire in them. (Gen. Morph. ii. 242.) 

No less interesting and instructive than homochromic 
selection is that species of natural selection which Darwin 
calls "sexual selection" which explains the origin of the 
so-called " secondary sexual characters." We have already 
mentioned these subordinate sexual characteristics, so in- 
structive in many respects. They comprise those pecu- 
liarities of animals and plants which belong only to one 
of the two sexes, and which do not stand in any direct 
relation to the act of propagation itself (compare above, 
p. 244). Such secondary sexual characters occur in great 
variety among animals. We all know how striking is the 
difference of the two sexes in size and colour in many birds 
and butterflies. The male sex is generally the larger and 
more beautiful. It often possesses special decorations or 
weapons ; as for example, the spur and comb of the cock, 
the antlers of the stag and deer, etc. All these peculiarities 
of the two sexes have nothing directly to do with pro- 
pagation itself, which is effected by the "primary sexual 
characters," or actual sexual organs. 

Now, the origin of these remarkable " secondary sexual 
characters " is explained by Darwin simply by a choice or 


selection which takes place in the propagation of animals. 
In most animals the number of individuals of both sexes is 
unequal ; either the number of the female or the number 
of the male individuals is greater, and, as a rule, when 
the season of propagation approaches, a struggle takes 
place between the rivals for the possession of the animals 
of the other sex. It is well known with what vigour and 
vehemence this struggle is fought out among the higher 
animals — among mammals and birds — especially among those 
of polygamous habits. Among gallinaceous birds, where for 
one cock there are several hens, a severe struggle takes place 
between the competing cocks for as large a harem as possible. 
The same is the case with many ruminating animals. 
Among stags and deer, for instance, at the period of rut, 
deadly struggles take place between the males for the 
possession of the females. The secondary sexual character 
which here distinguishes the males — the antlers of stags 
and deer — not possessed by the female, is, according to 
Darwin, the consequence of that struggle. Here the motive 
and cause determining the struggle is not, as in the case of 
the struggle for individual existence, serf-preservation, but 
the preservation of the species — propagation. There are 
numerous passive weapons of defence, as well as active 
weapons for attack. The lion's mane, not possessed by the 
female, is evidently such a weapon of defence ; it is an 
excellent means of protection against the bites which the 
male lions try to inflict on each other's necks when fighting 
for the females ; consequently those males with the strongest 
manes have the greatest advantage in the sexual struggle. 
The dewlap of the ox and the comb of the cock are similar 
defensive weapons. Active weapons of attack, on the other 


hand, are the antlers of the stag, the tusks of the boar, the 
spur of the cock, and the hugely developed pair of jaws in 
the male stag-beetle ; all are instruments employed by the 
males in the struggle for the females, for annihilating or 
chasing away their rivals. 

In the cases just mentioned, it is the bodily " struggle to 
the death" which determines the origin of the secondary 
sexual characters. But, besides these mortal struggles, there 
are other important competitions in sexual selection, which 
no less influence the structure of the rivals. These consist 
principally in the fact that the courting sex tries to please 
the other by external finery, by beauty of form, or by a 
melodious voice. Darwin thinks that the beautiful voices 
of singing birds have principally originated in this way. 
Many male birds carry on a regular musical contest when 
they contend for the possession of the females. It is known 
of several singing birds, that in the breeding season the 
males assemble in numbers round the females, and let their 
songs resound before them, and that then the females choose 
the singers who best please them for their mates. Among 
other songsters, individual males pour out their songs in the 
loneliness of the forest in order to attract the females, and 
the latter follow the most attractive calls. A similar musical 
contest, though certainly less melodious, takes place among 
crickets and grasshoppers. The male cricket has on its belly 
two instruments like drums, and produces with these the 
sharp chirping notes which the ancient Greeks curiously 
enough thought beautiful music. Male grasshoppers, partly 
by using their hind-legs like the bow of a violin against 
their wing coverings, and partly by rubbing their wing 
coverings together, bring out tones which are, indeed, not 


melodious to us, but which please the female grasshoppers 
so much that they choose the male who fiddles the best. 

Among other insects and birds it is not song or, in fact, 
any musical accomplishment, but finery or beauty of the 
one sex which attracts the other. Thus we find that, among 
most gallinaceous birds, the cocks are distinguished by combs 
on their heads, or by a beautiful tail, which they can spread 
out like a fan ; as for example, in the case of the peacock 
and turkey-cock. The magnificent tail of the bird of para- 
dise is also an exclusive ornament of the male sex. In like 
manner, among very many other birds and very many 
insects, principally among butterflies, the males are dis- 
tinguished from the females by special colours or other 
decorations. These are evidently the results of sexual 
selection. As the females do not possess these attractions 
and decorations, we must come to the conclusion that they 
have been acquired by .degrees by the males in the competi- 
tion for the females, which takes its origin in the selective 
discrimination of the females. 

We may easily picture to ourselves, in detail, the ap- 
plication of this interesting conclusion to the human com- 
munity. Here, also, the same causes have evidently in- 
fluenced the development of the secondary sexual characters. 
The characteristics distinguishing the man, as well as those 
distinguishing the woman, owe their origin, certainly for the 
most part, to the sexual selection of the other sex. In an- 
tiquity and in the Middle Ages, especially in the romantic 
age of chivalry, it was the bodily struggles to the death — the 
tournaments and duels — which determined the choice of the 
bride ; the strongest carried home the bride. In more recent 
times, however, in our so-called " polished " or " highly civil- 


ized " society, competing rivals prefer to contend indirectly 
by means of musical accomplishments, instrumental per- 
formances and song, by bodily charms, natural beauty, or 
artificial decoration. But by far the most important of these 
different forms of sexual selection in man is that form which 
is the most exalted, namely, psychical selection, in which the 
mental exceUencies of the one sex influence and determine 
the choice of the other. The most highly intellectually de- 
veloped types of men have, throughout generations, when 
choosing a partner in life, been guided by her excellencies of 
soul, and have thus transmitted these qualities to their pos- 
terity, and they have in this way, more than by any other 
thing, helped to create the deep chasm which at present 
separates civilized men from the rudest savages, and from 
our common animal ancestors. In fact, both the part played 
by the prevalence of a higher standard of sexual selection, 
and the part played by the due division of labour between 
the two sexes, is exceedingly important, and I believe that 
here we must seek for the most powerful causes which have 
determined the origin and the historical development of the 
races of man. (GJ-en. Morph. ii. 247.) As Darwin, in his 
exceedingly interesting work, published in 1871, on " The 
Descent of Man and Sexual Selection," 48 has discussed this 
subject in the most masterly manner, and has iUustrated 
it by most remarkable examples, I refer for further detail 
to that work. 

But now let us look again at two extremely important 
organic laws which can be explained by the theory of 
selection, as necessary consequences of natural selection 
in the struggle for existence. I mean the law of division 
of labour, or differentiation, and the law of progress, or 


'perfecting. When the phenomena due to these two laws 
first became known, through observation of the historical de- 
velopment, the individual development, and the comparative 
anatomy of animals and plants, naturalists were inclined to 
trace them to a direct creative influence. It was supposed to 
be part of the plan of the Creator, acting for a definite purpose, 
in the course of time to develop the forms of animals and 
plants more and more variously, and to bring them more and 
more to a state of perfection. We shall evidently make a great 
advance in the knowledge of nature if we reject thisteleological 
and anthropomorphic conception, and if we can prove the two 
laws of Division of Labour and Perfecting to be the necessary 
consequences of natural selection in the struggle for life. 

The first great law which follows directly and of necessity 
from natural selection, is that of separation, or differentia- 
tion, which is frequently called division of labour, or poly- 
morphism, and which Darwin speaks of as divergence of 
character. (Gen. Morph. ii. 249). We understand by it the 
general tendency of all organic individuals to develop them- 
selves more and more diversely, and to deviate from the 
common primary type. The cause of this general inclination 
towards differentiation and the formation of heterogeneous 
forms from homogeneous beginnings is, according to Darwin, 
simply to be traced to the circumstance that the struggle for 
life between every two organisms rages all the more fiercely 
the nearer the relation in which they stand to one another, 
or the more nearly alike they are. This is an exceedingly 
important, and in reality an exceedingly simple relation, 
but it is usually not duly considered. 

It must be obvious to every one, that in a field of a 
certain size, besides the corn-plants which have been sown, a 


great number of weeds can exist, and, moreover, in places 
which could not have been occupied by corn-plants. The 
more dry and sterile places of the ground, in which no corn- 
plant would thrive, may still furnish sustenance to weeds of 
different kinds ; and such species and individuals of weeds 
will more readily be able to exist in such conditions, in pro- 
portion as they are suited to adapt themselves to the dif- 
ferent parts of the ground. It is the same with animals. It 
is evident that a much greater number of animal indivi- 
duals can live together in one and the same limited district, if 
they are of various and different natures, than if they 
are all alike. There are trees (for example, the oak) on 
which a couple of hundred of different species of insects live 
together. Some feed on the fruits of the tree, others on the 
leaves, others again on the bark, the root, etc. It would be 
quite impossible for an equal number of individuals to live 
on this tree if all were of one species ; if, for example, all fed 
on the bark, or only upon the leaves. Exactly the same is 
the case in human society. In one and the same small town, 
only a certain number of workmen can exist, even when 
they follow different occupations. The division of labour, 
which is of the greatest use to the whole community, as well 
as to the individual workman, is a direct consequence of the 
struggle for life, of natural selection ; for this straggle can 
be sustained more easily the more the activities, and hence, 
also, the forms of the different individuals deviate from 
one ■ another. The different function naturally produces its 
reaction in changing the form, and the physiological divi- 
sion of labour necessarily determines the morphological 
differentiation, that is, the " divergence of character." 37 
Now, I beg the reader again to remember that all species 


of animals and plants are variable, and possess the capability 
of adapting themselves to different places or to local rela- 
tions. The varieties or races of each species, according to 
the laws of adaptation, deviate all the more from the original 
primary species, the greater the difference of the new con- 
ditions to which they adapt themselves. If we imagine 
these varieties — which have proceeded from a common 
primary form — to be disposed in the shape of a branching, 
radiating bunch, then those varieties will be best able to 
exist side by side and propagate which are most distant 
from one another, which stand at the ends of the series, or 
at the opposite sides of the bunch. Those forms, on the 
other hand, occupying a middle position — presenting a state 
of transition — have the most difficult position in the struggle 
for life. The necessaries of life differ most in the two ex- 
tremes, in the varieties most distant from one another, and 
consequently these will get into the least serious conflict 
with one another in the general struggle for life. But the 
intermediate forms, which have deviated less from the 
original primary form, require nearly the same neces- 
saries of life as the original form, and therefore, in com- 
peting for them, they will have to struggle most with, and be 
most seriously threatened by, its members. Consequently, 
when numerous varieties of a species live side by side on the 
same spot of the earth, the extremes, or those forms deviating 
most from one another, can much more easily continue to 
exist beside one another than the intermediate forms which 
have to struggle with each of the different extremes. The 
intermediate forms will not be able to resist, for any length 
of time, the hostile influences which the extreme forms 
victoriously overcome. These alone maintain and propagate 


themselves, and at length cease to be any longer connected 
with the original primary species through intermediate forms 
of transition. Thus arise " good species " out of varieties. 
Thus, then, the struggle for life necessarily favours the 
general divergence of organic forms, that is, the constant 
tendency of organisms to form new species. This fact does 
not rest upon any mystic quality, or upon an unknown forma- 
tive tendency, but upon the interaction of Inheritance and 
Adaptation in the struggle for life. As the intermediate 
forms, that is, the individuals in a state of transition, of 
the varieties of every species die out and become extinct, 
the process of divergence constantly goes further, and from 
the extremes forms develop which we distinguish as new 

Although all naturalists have been obliged to acknowledge 
the variability and mutability of all species of animals and 
plants, yet most of them have hitherto denied that the 
modification or transformation of the organic form surpasses 
the original limit of the characters of the species. Our 
opponents cling to the proposition — " However far a species 
may exhibit deviations from its usual form in a collection of 
varieties, yet the varieties of it are never so distinct from 
one another as two really good species." This assertion, 
which Darwin's opponents usually place at the head of 
their arguments, is utterly untenable and unfounded. 
This will become quite clear as soon as we critically 
compare the various attempts to define the idea of species. 
No naturalist can answer the question as to what is in 
reality a " genuine or good species " (" bona species ") ; yet 
every systematic naturalist uses this expression every day, 
and whole libraries have been written on the question as to 

VOL. I. T 


whether this or that observed form is a species or a variety, 
whether it is a really good or a had species. The most 
general answer to this question used to be the following : 
" To one species belong all those individuals which agree in 
all essential characteristics. Essential characteristics of 
species are those which remain permanent or constant, and 
never become modified or vary." But as soon as a case 
occurred in which the characteristic — which had hitherto 
been considered essential — did become modified, then it was 
said, " This characteristic is not essential to the species, for 
essential characteristics never vary." Those who argued 
thus evidently moved in a circle, and the naivete' with 
which this circular method of defining species is laid down 
in thousands of books as an unassailable truth, and is still 
constantly repeated, is truly astonishing. 

All other attempts which have been made to arrive at a 
definite and logical determination of the idea of organic 
" species " have, like the last, been utterly futile, and led to 
no results. Considering the nature of the case, it cannot be 
otherwise. The idea of species is just as truly a relative 
one and not absolute, as is the idea of variety, genus family, 
order, class, etc. I have proved this in detail in the criti- 
cism of the idea of species in my " General Morphology " 
(Gen. Morph. ii. 323-364). I will waste no more time on 
this unsatisfactory discussion, and now only add a few 
words about the relation of species to hybridism. Formerly 
it was regarded as a dogma, that two good species could 
never produce hybrids which could reproduce themselves as 
such. Those who thus dogmatized almost always appealed 
to the hybrids of a horse and donkey, the mule and the 
hinny, which, truly enough, are seldom able to reproduce 


themselves. But the truth is that such unfruitful hybrids 
are rare examples, and in the majority of cases hybrids of 
two totally different species are fruitful and able to repro- 
duce themselves. They can almost always fruitfully mix 
with one or other of the parent species, and sometimes 
also among themselves ; and in this way completely new 
forms can originate according to the laws of " mixed trans- 
mission by inheritance." 

Thus, in fact, hybridism is a source of the origin of new 
species, distinct from the source we have hitherto considered 
— natural selection. I have already spoken occasionally of 
these hybrid species (species hybridae), especially of the 
hare-rabbit (Lepus Darwinii), which has arisen from the 
crossing of a male hare and a female rabbit ; the goat- 
sheep (Capra ovina), which has arisen from the pairing of 
a he-goat and ewe ; also the different species of thistles 
(Cirsium), brambles (Rubus), etc. It is possible that 
many wild species have originated in this way, as even 
Linnaeus assumed. At all events, these hybrid species, 
which can maintain and propagate themselves as well as 
pure species, prove that hybridism cannot serve in any way 
to give an absolute definition to the idea of species. 

I have already mentioned (p. 47) that the many vain 
attempts to define the idea of species theoretically have 
nothing whatever to do with the practical distinction of 
species. The extensive practical application of the idea of 
species, as it is carried out in systematic zoology and botany, 
is very instructive as furnishing an example of human folly. 
Hitherto, by far the majority of zoologists and botanists, in 
distinguishing and describing the different forms of animals 
and plants, have endeavoured, above all things, to dis- 


tinguish accurately kindred forms as so many "good 
species." However, it has been found scarcely possible, in 
any group, to make an accurate and consistent distinction 
of such "genuine or good species." There are no two 
zoologists, no two botanists, who agree in all cases as 
to which of the nearly related forms of a genus are good 
species, and which are not. All authors have different 
views about them. In the genus Hieracium, for example, 
one of the commonest genera of European plants, no less 
than 300 species have been distinguished in Germany alone. 
The botanist Fries, however, only admits 106, Koch only 52, 
as "good species," and others accept scarcely 20. The 
differences in the species of brambles (Rubus) are equally 
ffreat. Where one botanist makes more than a hundred 
species, a second admits only about one half of that number, 
a third only five or six, or even fewer species. The birds of 
Germany have long been very accurately known. Bechstein, 
in his careful " Natural History of German Birds," has dis- 
tinguished 367 species, L. Reichenbach 379, Meyer and Wolff 
406, and Brehm, a clergyman learned in ornithology, dis- 
tinenishes even more than 900 different species. 

Thus we see that here, and, in fact, in every other domain 
of systematic zoology and botany, the most arbitrary pro- 
ceedings prevail, and, from the nature of the case, must 
prevail. For it is quite impossible accurately to distinguish 
varieties and races from so-called " good species." Varieties 
are commencing species. The variability or adaptability of 
species, under the influence of the struggle for life, necessi- 
tates the continual and progressive separation or differentia- 
tion of varieties, and the perpetual delimitation of new forms. 
Whenever these are maintained throughout a number of 


generations by inheritance, whilst the intermediate forms 
die out, they form independent " new species." The origin 
of new species by division of labour, or separation, diver- 
gence, or differentiation of varieties, is therefore a necessary 
consequence of natural selection. 37 

The same kind of interest attaches to a second great law 
which we deduce from natural selection, and which is, indeed, 
closely connected with the law of Divergence, but in no way 
identical with it ; namely, the law of Progress (progressus), 
or Perfecting (teleosis). (Gen. Morph. ii. 257). This great 
and important law, like the law of differentiation, had 
long been empirically established by palneontological ex- 
perience, before Darwin's Theory of Selection gave us the 
key to the explanation of its cause. The most distinguished 
palaeontologists have pointed out the law of progress as the 
most general result of their investigations of fossil organisms. 
This has been specially done by Bronn, whose investiga- 
tions on the laws of construction 1S and the laws of the 
development 19 of organisms, although little heeded, are 
excellent, and deserve most careful consideration. The 
general results of the law of differentiation and the law of 
progress, at which Bronn arrived by a purely mechanical 
hypothesis, and by exceedingly accurate, laborious, and care- 
ful investigations, are brilliant confirmations of the truth of 
these two great laws which we deduce as necessary in- 
ferences from the theory of selection. 

The law of progress or of perfecting establishes the ex- 
ceedingly important fact, on the ground of palseontologi- 
cal experience, that in successive periods of this earth's 
history, a continual increase in the perfection of organic 
formations has taken place. Since that inconceivably 


remote period in which life on our planet began with the 
spontaneous generation of Monera, organisms of all groups, 
both collectively as well as individually, have continually 
become more perfectly and highly developed. The steadily 
increasing variety of living forms has always been accom- 
panied by progress in organization. The lower the strata 
of the earth in which the remains of extinct animals and 
plants lie buried, that is, the older the strata are, the more 
simple and imperfect are the forms which they contain. This 
applies to organisms collectively, as well as to every single 
large or small group of them, setting aside, of course, those 
exceptions which are due to the process of degeneration, 
which we shall discuss hereafter. 

As a confirmation of this law I shall mention only the 
most important of all animal groups, the tribe of vertebrate 
animals. The oldest fossil remains of vertebrate animals 
known to us belong to the lowest class, that of Fishes. Upon 
these there followed later more perfect Amphibious animals, 
then Reptiles, and lastly, at a much later period, the most 
highly organized classes of vertebrate animals, Birds and 
Mammals. Of the latter only the lowest and most imperfect 
forms, without placenta, appeared at first, such as are the 
pouched animals (Marsupials), and afterwards, at a much 
later period, the more perfect mammals, with placenta. Of 
these, also, at first only the lower kinds appeared, the higher 
forms later ; and not until the late tertiary period did man 
gradually develop out of these last. 

If we follow the historical development of the vegetable 
kingdom we shall find the same law operative there. Of 
plants there existed at first only the lowest and most im- 
perfect classes, the Algse or tangles. Later there followed 


the group of Ferns or Filicinse (ferns, pole-reeds, scale- 
plants, etc.). But as yet there existed no flowering plants, 
or Phanerogama. These originated later with the Gynmo- 
sperms (firs and cycads), whose whole structure stands far 
below that of the other flowering plants (Angiosperms), and 
forms the transition from the group of fern-like plants to the 
Angiosperms. These latter developed at a still later date, 
and among them there were at first only flowering plants 
without corolla (Monocotyledons and Monochlamyds) ; only 
later were there flowering plants with a corolla (Dichlamyds). 
Finally, again, among these the lower polypetalous plants 
preceded the higher gamopetalous plants. The whole series 
thus constitutes an irrefutable proof of the great law of pro- 
gressive development. 

Now, if we ask what is the cause of this fact, we again, 
just as in the case of differentiation, come back to natural 
selection in the struggle for life. If once more we consider 
the whole process of natural selection, hew it operates 
through the complicated interaction of the different laws 
of Inheritance and Adaptation, we shall recognize not 
only divergence of character, but also the perfecting of 
structure to be the direct and necessary result of it. We 
can trace the same thing in the history of the human race. 
Here, too, it is natural and necessaiy that the progressive 
division of labour constantly furthers mankind, and urges 
every individual branch of human activity into new dis- 
coveries and improvements. This progress itself universally 
depends on differentiation, and is consequently, like it, a 
direct result of natural selection in the struggle for life. 




Laws of the Development of Mankind : Differentiation and Perfecting. 
— Mechanical Canse of these two Fundamental Laws. — Progress without 
Differentiation, and Differentiation without Progress. — Origin of 
Rudimentary Organs by Non-use and Discontinuance of Habit. — 
Ontogenesis, or Individual Development of Organisms. — Its General 
Importance. — Ontogeny, or the Individual History of Development of 
Vertebrate Animals, including Man. — The Fructification of the Egg. — 
Formation of the three Germ Layers. — History of the Development of 
the Central Nervous System, of the Extremities, of the Branchial 
Arches, and of the Tail of Vertebrate Animals. — Causal Connection and 
Parallelism of Ontogenesis and Phylogenesis, that is of the Development 
of Individuals and Tribes. — Causal Connection of the Parallelism of 
Phylogenesis and of Systematic Development. — Parallelism of the three 
Organic Series of Development. 

If man wishes to understand his position in nature, and 
to comprehend as natural facts his relations to the 
phenomena of the world cognisable by him, it is abso- 
lutely necessary that he should compare human with extra- 
human phenomena, and, above all, with animal phenomena. 
We have already seen that the exceedingly important 
physiological laws of Inheritance and Adaptation apply to 
the human organism in the same manner as to the animal 
and vegetable kingdoms, and in both cases interact with 
one another. Consequently, natural selection in the struggle 


for life acts so as to transform human society, just as 
it modifies animals and plants, and in both cases con- 
stantly produces new forms. The comparison of the phe- 
nomena of human and animal transformation is especially 
interesting in connection with the laws of divergence and 
progress, the two fundamental laws which, at the end of the 
last chapter, we proved to be direct and necessary conse- 
quences of natural selection in the struggle for life. 

A comparative survey of the history of nations, or what 
is called " universal history," will readily yield to us, as the 
first and most general result, evidence of a continually in- 
creasing variety of human activities, both in the life of in- 
dividuals and in that of families and states. This differenti- 
ation or separation, this constantly increasing divergence of 
human character and the form of human life, is caused by 
the ever advancing and more complete division of labour 
among individuals. While the most ancient and lowest 
stages of human civilization show us throughout the same 
rude and simple conditions, we see in every succeeding 
period of history, among different nations, a greater variety 
of customs, practices, and institutions. The increasing divi- 
sion of labour necessitates an increasing variety of forms 
corresponding to it. This is expressed even in the for- 
mation of the human face. Among the lowest tribes of 
nations, most of the individuals resemble one another so 
much that European travellers often cannot distinguish 
them at all. With increasing civilization the physiognomy 
of individuals becomes differentiated, and finally, among the 
most highly civilized nations, the English and Germans, 
the divergence in the characters of the face is so great that 
we very rarely mistake one face for another. 


The second great fundamental law which is obvious in the 
history of nations is the great law of progress or perfecting. 
Taken as a whole, the history of man is the history of his 
progressive development. It is true that everywhere and at 
all times we may notice individual retrogressions, or observe 
that crooked roads towards progress have been taken, which 
lead only towards one-sided and external perfecting, and 
thus deviate more and more from the higher goal of internal 
and enduring perfecting. However, on the whole, the 
movement of development of all mankind is and remains a 
progressive one, inasmuch as man continually removes him- 
self further from his ape-like ancestors, and continually 
approaches nearer to his own ideal. 

Now, if we wish to know what causes actually determine 
these two great laws of development in man, namely, the 
law of divergence and the law of progress, we must com- 
pare them with the corresponding laws of development in 
animals, and on a close examination we shall inevitably come 
to the conclusion that the phenomena, as well as their causes, 
are exactly the same in the two cases. The course of 
development in man, just as in that of animals, being 
directed by the two fundamental laws of differentiation 
and perfecting, is determined solely by purely mechanical 
causes, and is solely the necessary consequence of natural 
selection in the struggle for life. 

Perhaps in the preceding discussion the question has pre- 
sented itself to some — " Axe not these two laws identical ? 
Is not progress in all cases necessarily connected with diver- 
gence ? " This question has often been answered in the 
affirmative, and Carl Ernst Bar, for example, one of the 
greatest investigators in the domain of the history of de- 


velopment, has set forth the following proposition as one of 
the principal laws in the ontogenesis of the animal body : — 
" The degree of development (or perfecting) depends on 
the stage of separation (or differentiation) of the parts." 20 
Correct as this proposition may be on the whole, yet it is not 
universally true. In many individual cases it can be proved 
that divergence and progress by no means always coincide. 
Every progress is not a differentiation, and every differenti- 
ation is not a progress. 

Naturalists, guided by purely anatomical considerations, 
had already set forth the law relating to progress in organ- 
ization, that the perfecting of an organism certainly de- 
pends, for the most part, upon the division of labour among 
the individual organs and parts of the body, but that there 
are also other organic transformations which determine a 
progress in organization. One, in particular, which has 
been generally recognized, is the numerical diminution of 
identical parts. If, for example, we compare the lower 
articulated animals of the crustacean group, which possess 
numerous pairs of legs, with spiders which never have more 
than four pairs of legs, and with insects which always 
possess only three pairs of legs, we find this law, for 
which a great number of examples could be adduced, con- 
firmed. The numerical diminution of pairs of legs is a 
progress in the organization of articulated animals. In 
like manner the numerical diminution of corresponding 
vertebral joints in the trunk of vertebrate animals is a 
progress in their organization. Fishes and amphibious 
animals with a very large number of identical vertebral 
joints are, for this very reason, less perfect and lower than 
birds and mammals, in which the vertebral joints, as a 


whole, are not only very much more differentiated, but in 
which the number of corresponding vertebrae is also much 
smaller. Further, according to the same law of numerical 
diminution, flowers with numerous stamens are more 
imperfect than the flowers of kindred plants with a smaller 
number of stamens, etc. If therefore originally a great 
number of homogeneous parts exist in an organic body, and 
if, in the course of very many generations, this number be 
gradually decreased, this transformation will be an example 
of perfecting. 

Another law of progress, which is quite independent of 
differentiation, nay, even appears to a certain extent opposed 
to it, is the law of centralization. In general the whole 
organism is the more perfect the more it is organized as a 
unit, the more the parts are subordinate to the whole, and 
the more the functions and their organs are centralized. Thus, 
for example, the system of blood-vessels is most perfect 
where a centralized heart exists. In Hke manner, the dense 
mass of marrow which forms the spinal cord of vertebrate 
animals, and the ventral cord of the higher articulated 
animals, is more perfect than the decentralized chain of 
ganglia of the lower articulated animals, and the scattered 
system of ganglia in the molluscs. Considering the difficulty 
of explaining these complicated laws of progress in detail, I 
cannot here enter upon a closer discussion of them, and 
must refer to Bronn's excellent " Morphologischen Studien," 
and to my " General Morphology" (Gen. Morph. i. 370, 550 ; 
ii. 257-266). 

Just as we have become acquainted with phenomena of 
progress, quite independent of divergence, so we shall, on 
the other hand, very often meet with divergencies which 


are no perfecting, but which are rather the contrary, that 
is retrogressions or degenerations. It is easy to see that the 
changes which every species of animal and plant experi- 
ences cannot always be improvements. But rather many 
phenomena of differentiation, which are of direct advantage 
to the organism itself, are yet, in a wider sense, detrimental, 
inasmuch as they lessen its general capabilities. Frequently 
a relapse to simpler conditions of life takes place, and by 
adaptation to them a divergence in a retrograde direction. 
If, for instance, organisms which have hitherto lived inde- 
pendently accustom themselves to a parasitical life, they 
thereby degenerate or retrograde. Such animals, which 
hitherto had possessed a well-developed nervous system and 
quick organs of sense, as well as the power of moving freely, 
lose these when they accustom themselves to a parasitical 
mode of life ; they consequently retrograde more or less. 
There the differentiation viewed by itself is a degeneration, 
although it is advantageous to the parasitical organism. In 
the struggle for life such an animal, which has accustomed 
itself to live at the expense of others, by retaining its eyes 
and apparatus of motion, which are of no more use to it, 
would only expend so much material uselessly ; and when 
it loses these organs, then a great quantity of nourishment 
which was employed for the maintenance of these parts, 
benefits other parts. In the struggle for life between the 
different parasites, therefore, those which make least preten- 
sions will have advantage over the others, and this favours 
their degeneration. 

Just as this is found to be the case with the whole 
organism, so it is also with the parts of the body of an 
individual organism. A differentiation of parts, which 


leads to a partial degeneration, and finally even to the loss 
of individual organs, is, when looked at by itself, a degenera- 
tion, but yet may be advantageous to the organism in the 
struggle for life. It is easier to fight when useless baggage 
is thrown aside. Hence we meet everywhere, in the more 
highly-developed animal and vegetable bodies, processes of 
divergence, the essence of which is that they cause the 
degeneration, and finally the loss, of particular parts. And 
at this point the most important and instructive of all the 
series of phenomena bearing upon the history of organisms 
presents itself to us, namely, that of rudimentary or 
degenerate organs. 

It will be remembered that even in my first chapter I 
considered this exceedingly remarkable series of phe- 
nomena, from a theoretical point of view, as one of the 
most important and most striking proofs of the truth 
of the doctrine of descent. We designated as rudimentary 
organs those parts of the body which are arranged for a 
definite purpose and yet are without function. Let me 
remind the reader of the eyes of those animals which 
live in the dark in caves and underground, and which con- 
sequently never can use them. In these animals we find 
real eyes hidden under the skin, frequently developed 
exactly as are the eyes of animals which really see ; 
and yet these eyes never perform any function, indeed 
cannot, simply for the reason that they are covered by 
an opaque membrane, and consequently no ray of light 
falls upon them (compare above, p. 13). In the ancestors 
of these animals, which lived in open daylight, the eyes 
were well developed, covered by a transparent horny 
capsule (cornea), and actually served the purpose of 


seeing. But as the animals gradually accustomed them- 
selves to an underground mode of life, and withdrew from 
the daylight and no longer used their eyes, these became 

Very clear examples of rudimentary organs, moreover, are 
the wings of animals which cannot fly ; for example, the 
wings of the running birds, like the ostrich, emeu, casso- 
wary, etc., the legs of which have become exceedingly 
developed. These birds having lost the habit of flying, have 
consequently lost the use of their wings ; however, the 
wings are still there, although in a crippled form. We very 
frequently find such crippled wings in the class of insects, 
most members of which can fly. 

From reasons derived from comparative anatomy and 
other circumstances, we can with certainty draw the 
inference that all insects now living (all dragon-flies, grass- 
hoppers, beetles, bees, bugs, flies, butterflies, etc.) have 
originated from a single common parental form, from a 
primary insect which possessed two well-developed pairs 
of wings, and three pairs of legs. Yet there are very many 
insects in which either one or both pairs of wings have 
become more or less degenerated, and many in which they 
have even completely disappeared For example, in the whole 
order of flies, or Diptera, the hinder pair of wings — in the 
bee-parasites, or Strepsiptera, on the other hand, the fore pair 
of wings — have become degenerated or entirely disappeared. 
Moreover, in every order of insects we find individual 
genera, or species, in which the wings have more or less 
degenerated or disappeared. The latter is the case espe- 
cially in parasites. The females have frequently no wings, 
whereas the males have ; for instance, in the case of glow- 


•worms (Lampyris), Strepsiptera, etc. This partial or com- 
plete degeneration of the wings of insects has evidently- 
arisen from natural selection in the struggle for life. For 
we find insects without wings living under circumstances 
where flying would be useless, or even decidedly injurious 
to them. If, for example, insects living on islands fly about 
much, it may easily happen that when flying they are blown 
into the sea by the wind, and if (as is always the case) 
the power of flying is differently developed in different 
individuals, then those which fly badly have an advantage 
over those which fly well ; they are less easily blown into 
the sea, and remain longer in life than the individuals of the 
same species which fly well. In the course of many 
generations, by the action of natural selection, this cir- 
cumstance must necessarily leads to a complete suppression 
of the wings. If this conclusion had been arrived at on 
purely theoretical grounds, we might be pleased to find its 
truth established by facts. For upon isolated islands the 
proportion of wingless insects to those possessing wings is 
surprisingly large, much larger than among the insects 
inhabiting continents. Thus, for example, according to 
Wollaston, of the 550 species of beetles which inhabit the 
island of Madeira, 220 are wingless, or possess such imperfect 
wings that they can no longer fly ; and of the 29 genera 
which belong to that island exclusively, no less than 23 con- 
tain such species only. It is evident that this remarkable 
circumstance does not need to be explained by the special 
wisdom of the Creator, but is sufficiently accounted for by 
natural selection, because in this case the hereditary disuse 
of the wings, the discontinuance of flying in the presence 
of dangerous winds, has been very advantageous in the 


struggle for life. In cither wingless insects the want of 
wings has been advantageous for other reasons. Viewed 
by itself, the loss of wings is a degeneration, but in these 
special conditions of life it is advantageous to the organism 
in the struggle for life. 

Among other rudimentary organs I may here, by way of 
example, further mention the lungs of serpents and serpent- 
like lizards. All vertebrate animals possessing lungs, such 
as amphibious animals, reptiles, birds, and mammals, have a 
pair of lungs, a right and a left one. But in cases where the 
body is exceedingly thin and elongated, as in serpents and 
serpent-like lizards, there is no room for the one lung by the 
side of the other, and it is an evident advantage to the 
mechanism of respiration if only one lung is developed. A 
single large lung here accomplishes more than two small ones 
side by side would do ; and consequently, in these animals, we 
invariably find only the right or only the left lung fully 
developed The other is completely aborted, although existing 
as a useless rudiment. In like manner, in all birds the right 
ovary is aborted and without function ; only the left one is 
developed, and yields all the eggs. 

I mentioned in the first chapter that man also possesses 
such useless and superfluous rudimentary organs, and I 
specified as such the muscles which move the ears. Another 
of them is the rudiment of the tail which man possesses in 
his 3 — 5 tail vertebrae, and which, in the human embryo, 
stands out prominently during the first two months of its 
development (compare Plates II. and III,). It afterwards 
becomes completely hidden. The rudimentary little tail of 
man is an irrefutable proof of the fact that he is descended 
from tailed ancestors. In woman the tail is generally 

vol. r. u 


by one vertebra longer than in man. There still exist 
rudimentary muscles in the human tail which formerly 
moved it. 

Another case of human rudimentary organs, only belong- 
ing to the male, and which obtains in like manner in all male 
mammals, is furnished by the mammary glands on the 
breast, which, as a rule, are active only in the female sex. 
However, cases of different mammals are known, especially 
of men, sheep, and goats, in which the mammary glands 
were fully developed in the male sex, and yielded milk as 
food for their offspring. I have already mentioned before 
(p. 12) that the rudimentary auricular muscles in man can 
still be employed to move their ears, by some persons who 
have perseveringly practised them. In fact, rudimentary 
organs are frequently very differently developed in different 
individuals of the same species ; in some they are tolerably 
large, in others very small. This circumstance is very im- 
portant for their explanation, as is also the other circum- 
stance that generally in embryos, or in a very early period 
of life, they are much larger and stronger in proportion to 
the rest of the body than they are in fully developed and 
fully grown organisms. This can, in particular, be easily 
pointed out in the rudimentary sexual organs of plants 
(stamens and pistil), which I have already mentioned. They 
are proportionately much larger in the young flower-bud 
than in the mature flower. 

I have remarked (p. 15) that rudimentary or suppressed 
organs were the strongest supports of the monistic or 
mechanical conception of the universe. If its opponents, the 
dualists and teleologists, understood the immense signifi- 
cance of rudimentary organs, it would j ut them into a state 


of despair. Their ludicrous attempts to explain that rudi- 
mentary organs were given to organisms by the Creator " for 
the sake of symmetry/' or " as a formal provision," or " in 
consideration of his general plan of creation," sufficiently 
prove the utter impotence of their perverse conception of 
the universe. I must here repeat that, even if we knew 
absolutely nothing of the other phenomena of development, 
we should be obliged to believe in the truth of the Theory of 
Descent, solely on the ground of the existence of rudimentary 
organs. Not one of its opponents has been able to throw 
even a feeble glimmer of an acceptable explanation upon 
these exceedingly remarkable and important phenomena. 
There is scarcely any highly developed animal or vegetable 
form which has not some rudimentary organs, and in most 
cases it can be shown that they are the products of natural 
selection, and that they have become suppressed by disuse. 
It is the reverse of the process of formation in which new 
organs arise from adaptation to certain conditions of life, and 
by the use of parts as yet incompletely developed. It is true 
our opponents usually maintain that the origin of altogether 
new parts is completely inexplicable by the Theory of 
Descent. However, I distinctly assert that to those who 
possess a knowledge of comparative anatomy and physiology 
this matter does not present the slightest difficulty. Every 
one who is familiar with comparative anatomy and the 
history of development will find as little difficulty about 
the origin of completely new organs as about the utter disap- 
pearance of rudimentary organs. The disappearance of the 
latter, viewed by itself, is the converse of the origin of the 
former. Both processes are particular phenomena of differ- 
entiation, which, like all others, can be explained quite 


simply and mechanically by the action of natural selection 
in the struggle for life. 

The infinitely important study of rudimentary organs and 
their origin, the comparison of their palteontological and 
embryological development, now naturally leads us to the 
consideration of one of the most important and instructive 
of all biological phenomena, namely, the parallelism which 
the phenomena of progress and divergence present to us in 
three different series. When, in the last chapter, we spoke 
of perfecting and division of labour, we understood by 
those words progress and separation, and those changes 
effected by them, which in the long and slow course of the 
earth's history have led to a continual variation of the 
flora and fauna, to the origin of new and to the disappear- 
ance of ancient species of animals and plants. Now, 
if we follow the origin, the development, and the life 
of every single organic individual, we meet with exactly 
the same phenomena of progress and differentiation. The 
individual development, or the ontogenesis of every single 
organism, from the egg to the complete form is nothing 
but a growth attended by a series of diverging and pro- 
gressive changes. This applies equally to animals, plants, 
and protista. If, for example, we consider the ontogeny 
of any mammal, of man, of an ape, or of a pouched 
animal, or if we follow the individual development of any 
other vertebrate animal of another class, we everywhere 
find essentially the same phenomena. Every one of 
these animals develops itself originally out of a single cell, 
the egg. This cell increases by self-division, and forms a 
number of cells, and by the growth of this accumulation of 
cells, by the divergent development of originally identical 


cells, by the division of labour among them, and by their 
perfecting, there arises the perfect organism, the compli- 
cated composition of which excites our admiration. 

It seems to me here indispensable to draw attention 
more closely to those infinitely important and interesting 
processes which accompany ontogenesis, or the individual 
development of organisms, and especially to that of verte- 
brate animals, man included. I wish especially to recom- 
mend these exceedingly remarkable and instructive phe- 
nomena to the reader's most careful consideration, first, 
because they are among the strongest supports of the Theory 
of Descent, and secondly, because, considering their immense 
general importance, they have hitherto been properly con- 
sidered only by a few privileged persons. 

We cannot indeed but be astonished when we consider 
the deep ignorance which still prevails, in the widest circles, 
about the facts of the individual development of man and 
organisms in general. These facts, the universal importance 
of which cannot be estimated too highly, were established, 
in their most important outlines, even more than a hundred 
years ago, in 1759, by the great German naturalist Caspar 
Friedriech Wolff, in his classical " Theoria Generationis." 
But, just as Lamarck's Theory of Descent, founded in 1809, 
lay dormant for half a century, and was only awakened to 
new and imperishable life in 1859, by Darwin, in like 
manner Wolffs Theory of Epigenesis remained unknown for 
nearly half a century ; and it was only after Oken, in 1806, 
had published his history of the development of the in- 
testinal tube, and after Meckel, in 1812, had translated 
Wolffs work (written in Latin) on the same subject into 
German, that Wolffs theory of epigenesis became more gener- 


ally known, and formed the foundation of all subsequent 
investigations of the history of individual development, 
The study of ontogenesis now received a great stimulus, and 
soon there appeared the classical investigations of the two 
friends, Christian Pander (1817) and Carl Ernst Bar (1819). 
Bar, in his remarkable " Entwickelungsgeschichte der 
Thiere," 20 worked out the ontogeny of vertebrate ani- 
mals in all its important facts. He carried out a series of 
such excellent observations, and illustrated them by such 
profound philosophical reflections, that his work became 
the foundation for a thorough understanding of this im- 
portant group of animals, to which, of course, man also 
belongs. The facts of embryology alone would be suffi- 
cient to solve the question of man's position in nature, which 
is the highest of all problems. Look attentively at and 
compare the eight figures which are represented on the ad- 
joining Plates II. and III., and it will be seen that the 
philosophical importance of embryology cannot be too 
highly estimated. 

We may well ask, What do our so-called " educated " 
circles, who think so much of the high civilization of the 
19th century, know of these most important biological facts, 
of these indispensable foundations for understanding their 
own organism ? How much do our speculative philosophers 
and theologians know about them, who fancy they can arrive 
at an understanding of the human organism by mere guess- 
work or divine inspiration ? What indeed do the majority of 
naturalists, not excepting the majority of the so-called "zool- 
ogists " (including the entomologists !), know about them ? 

The answer to this question tells much to the shame of 
the persons above indicated, and we must confess, willingly 


or unwillingly, that these invaluable facts of human ontogen}- 
are, even at the present day, utterly unknown to most 
people, or are in no way valued as they deserve to be. It is 
in the face of such a condition of things as this that we see 
clearly upon what a wrong and one-sided road the much 
vaunted culture of the 19th century still moves. Ignorance 
and superstition are the foundations upon which most men 
construct their conception of their own organism and its rela- 
tion to the totality of things ; and these palpable facts of 
the history of development, which might throw the light 
of truth upon them, are ignored. It is true these facts are 
not calculated to excite approval among those who assume a 
thorough difference between man and the rest of nature, and 
who will not acknowledge the animal origin of the human 
race. That origin must be a very unpleasant truth to 
members of the ruling and privileged castes in those nations 
among which there exists an hereditary division of social 
classes, in consequence of false ideas about the laws of in- 
heritance. It is well known that, even in our day, in many 
civilized countries the idea of hereditary grades of rank 
goes so far, that, for example, the aristocracy imagine them- 
selves to be of a nature totally different from that of or- 
dinary citizens, and nobles who commit a disgraceful 
offence are punished by being expelled from the caste of 
nobles, and thrust down among the pariahs of "vulgar 
citizens." What are these nobles to think of the noble blood 
which flows in their privileged veins, when they learn that 
all human embryos, those of nobles as well as commoners, 
during the first two months of development, are scarcely 
distinguishable from the tailed embryos of dogs and other 
mammals ? 


As the object of these pages is solely to further the 
general knowledge of natural truths, and to spread, in wider 
circles, a natural conception of the relations of man to the 
rest of nature, I shall be justified if I do not pay any 
regard to the widely-spread prejudice in favour of an ex- 
ceptional and privileged position for man in creation, and 
simply give here the embryological facts from which the 
reader will be able to draw conclusions affirming the 
groundlessness of those prejudices. I wish all the more 
to entreat him to reflect carefully upon these facts of on- 
togeny, as it is my firm conviction that a general knowledge 
of them can only promote the intellectual advance, and 
thereby the mental perfecting, of the human race. 

Amidst all the infinitely rich and interesting material 
which lies before us in the ontogeny of vertebrate animals, 
that is, in the history of their individual development, I shall 
here confine myself to showing some of those facts which 
are of the greatest importance to the Theory of Descent in 
general, as well as in its special application to man. Man 
is at the beginning of his individual existence a simple egg, 
a single little cell, just the same as every animal organism 
which originates by sexual generation. The human egg is 
essentially the same as that of all other mammals, and can- 
not be distinguished from the egg of the higher mammals. 
The egg represented in Fig. 5 might be that of a man or an 
ape as well as of a dog, a horse, or any other mammal. Not 
only the form and structure, but even the size of the egg in 
most mammals is the same as in man, namely, about the 
120th part of an inch in diameter, so that the egg under 
favorable circumstances, with the naked eye, can just be 
perceived as a small speck. The differences which really 


exist between the eggs of different mammals and that of 
man do not consist in the form, but in the chemical mixture, 
in the molecular composition of the albuminous combination 
of carbon, of which the egg essentially consists. These 
minute individual differences of all eggs, which depend upon 
indirect or potential adaptation (and especially upon the 
law of individual adaptation), are indeed not directly per- 
ceptible to the exceedingly imperfect senses of man, but are 
cognisable through indirect means, as the primary causes of 
the difference of all individuals. 

The human egg is, like that of all other mammals, a 
small globular bladder, which contains all the constituent 
parts of a simple organic cell (Fig. 5). The most essential 

Fig. 6. — The human egg a hundred times en- 
larged. a. The kernel speck, or nucleolus (the 
so-called germinal spot of the egg), i. Kernel, 
or nucleus (the so-called germinal vesicle of the 
egg), c. Cell. substance, or protoplasm (so-called 
yolk of the egg) . d. Cell-membrane (the yolk- 
membrane of the egg ; in mammals, on account 
of its transparency, called zona pellucida) . The 
eggs of other mammals are of the same form. 

parts of it are the mucous cell-substance, or the protoplasma 
(c), which in an egg is called the "yolk," and the cell-kernel, 
or nucleus (6), surrounded by it, which is here called by the 
special name of the " germinal vesicle." The latter is a deli- 
cate, clear, glassy globule of albumen, of about l-600th part of 
an inch in diameter, and surrounds a still smaller, sharply- 
marked, rounded granule (a), the kernel-speck, or the nucle- 
olus of the cell (in the egg it is called the " germinal spot "). 
The outside of the globular egg-cell of a mammal is sur- 
rounded by a thick pellucid membrane, the cell-membrane 


or yolk-membrane, which here bears the special name of 
zona pellucida (d). The eggs of many lower animals 
(for example of many Medusae) differ from this in being 
naked cells, as the outer covering, or cell-membrane, is 

As soon as the egg (ovulum) of the mammal has attained 
its full maturity, it leaves the ovary of the female, in which 
it originates, and passes into the oviduct, and through this 
narrow passage into the wider pouch or womb (uterus). If, 
meanwhile, the egg is fructified by the male seed (sperm), it 
develops itself in this pouch into an embryo, and does not 
leave it until perfectly developed and capable of coming 
into the world at birth as a young mammal. 

The variations of form and transformations which the 
fructified egg must go through within the uterus before it 
assumes the form of the mammal are exceedingly remark- 
able, and proceed from the beginning in man, in precisely 
the same way as in the other mammals. At first the fructi- 
fied egg of the mammal acts as a single-delled organism, 
which is about to propagate independently and increase 
itself; for example, an Amoeba (compare Fig. 2, p. 188). 
In point of fact the simple egg-cell becomes two, by the 
process of cell-division which I have previously described. 
There arise from the single germinal spot (the small kernel- 
speck of the original simple egg-cell) two new kernel-specks, 
and then in like manner, out of the germinal vesicle (the 
nucleus), two new cell-kernels. Then, and not until then, 
does the globular protoplasma first separate itself by an 
equatorial furrow into two halves, in such a manner that 
each half encloses one of the two kernels, together with 
its kernel-speck. Thus the simple egg-cell, within the 


original cellular membrane, has become two naked cells, 
each possessing its own kernel (Fig. 6). 

Fig. 6. — First commencement of the development of a mammal's egg, the 
so-called " yolk-cleavage " (propagation of the egg-cell by repeated self- 
division). A. The egg, by the formation of the first furrow, falls into two 
cells. JB. These by division fall into four cells. C. These latter have fallen 
into eight cells. D. By continued division a globular mass of numerous cells 
has arisen. 

The same process of cell-division now repeats itself 
several times in succession. In this way, from two cells 
(Fig. 6 i) there arise four (Fig. 6 B) ; from four, eight 
(Fig. 6 C) ; from eight, sixteen ; from these, thirty-two, etc. 
Each time the division of the kernel-speck precedes that of 
the kernel ; this, again, precedes that of the cell-substance, or 
protoplasma. As the division of the latter always com- 
mences with the formation of a superficial annular furroiv, 
or cleft, the whole process is usually called the furrowing of 
the egg, or yolk-cleavage, and the products of it, that is, the 
cells arising from the continued halving, are called the 
cleavage spheres. However, the whole process is nothing 
more than a simple, oft-repeated division of cells, and the 
products of it are actual, naked cells. Finally, through the 
continued division or " furrowing " of the mammal's egg, 
there arises a mulberry-shaped ball, which is composed of a 


great number of small spheres, naked cells, containing 
kernels (Fig. 6 D). These cells are the materials out of 
which the body of the young mammal is constructed. 
Every one of us has once been such a simple mulberry- 
shaped ball, composed only of small equi-formal cells. 

The further development of the globular lump of cells, 
which now represents the young body of the mammal, con- 
sists first in its changing into a globular bladder, as fluid 
accumulates within it. This bladder is called the germ- 
bladder (vesicula blastodermica). Its wall is at first com- 
posed of merely equi-formal cells. But soon, at one point on 
the wall, arises a disc-shaped thickening, as the cells here 
increase rapidly, and this thickening is now the foundation 
of the actual body of the germ or embryo, while the other 
parts of the germ-bladder serve only for its nutrition. The 
thickened disc, or foundation of the embryo, soon assumes an 
oblong, and then a fiddle-shaped form, in consequence of its 
right and left walls becoming convex (Fig. 7, p. 304). At 
this stage of development in the first form of their germ or 
embryo, not only all mammals, including man, but even all 
vertebrate animals in general — birds, reptiles, amphibious 
animals, and fishes — can either not be distinguished from 
one another at all, or only by very unessential differences, 
such as the arrangement of the egg-coverings. In all the 
whole body consists of nothing but a quite simple, oblong, 
oval, or violin-shaped thin disc, which is composed of three 
closely connected membranes or plates, lying one above 
another. Each of the three plates or layers of the germ 
consists simply of cells all exactly like one another; but 
each layer has a different function in the building up of the 
vertebrate animal body. Out of the upper or outer germ- 


layer arises solely the outer skin (epidermis), together 
with the central parts of the nervous system (spinal marrow 
and brain) ; out of the lower or inner layer arises only 
the inner delicate skin (epithelium) which lines the whole 
intestinal tube from the mouth to the anus, together with 
all the glands connected with it (lung, liver, salivary 
glands, etc) ; out of the middle germ-layer lying between 
the two others arise all the other organs, muscles, bones, 
blood-vessels. Now, the processes by which the various and 
exceedingly complicated parts of the fully-formed body of 
vertebrate animals arise out of such simple material — out of 
the three germ-layers composed only of cells — are, in the 
first place, the repeated division, and consequently the 
increase of cells ; in the second place, the division of labour 
or differentiation of these cells; and thirdly, the union of 
the variously developed or differentiated cells, for the 
formation of the different organs, Thus arises the gradual 
progress or perfecting which can be traced step by step 
in the development of the embryonic body. The simple 
embryonic cells, which are to constitute the body of the 
vertebrate animal, stand in the same relation to each other 
as citizens who wish to found a state. Some take to one 
occupation, others to another, and work together for the 
good of the whole. By this division of labour, or differen- 
tiation, and the perfecting (the organic progress) which is 
connected with it, it becomes possible for the whole state to 
accomplish undertakings which would have been impossible 
to the single individual. The whole body of the vertebrate 
animal, like every other many-celled organism, is a republi- 
can state of cells, and consequently it can accomplish organic 
functions which the individual cell, as a solitary individual 


(for example, an Amoeba, or a single-celled plant), could 
never perform. 

No sensible person supposes that carefully devised insti- 
tutions, which have been established for the good of the 
whole, as well as for the individual, in every human state, 
are the results of the action of a personal and supernatural 
Creator, acting for a definite purpose. On the contrary, 
every one knows that these useful institutions of organiza- 
tion in the state are the consequences of the co-operation of 
the individual citizens and their common government, as 
well as of adaptation to the conditions of existence of the 
outer world. Just in the same way we must judge of the 
many-celled organism. In it also all the useful arrangements 
are solely the natural and necessary result of the co-operation, 
differentiation, and perfecting of the individual citizens — 
the cells— and by no means the artificial arrangements of a 
Creator acting for a definite purpose. If we rightly consider 
this comparison, and pursue it further, we can distinctly 
see the perversity of that dualistic conception of nature 
which discovers the action of a creative plan of construction 
in the various adaptations of the organization of living 

Let us pursue the individual development of the verte- 
brate animal body a few stages further, and see what is next 
done by the citizens of this embryonic organism. In the 
central line of the violin-shaped disc, which is composed of 
the three cellular germ-layers, there arises a straight deli- 
cate furrow, the so-called " primitive streak," by which the 
violin-shaped body is divided into two equal lateral halves — 
a right and a left part or " antimer." On both sides of that 
.streak or furrow, the upper or external germ-layer rises in 


the form of a longitudinal fold, and both folds then grow 
together over the furrow in the central line, and thus form 


a cylindrical tube. This tube is called the marrow-tube, or 
medullary canal, because it is the foundation of the central 
nervous system, the spinal marrow (medulla spinalis). At 
first it is pointed both in front and behind, and it remains so 
for life in the lowest vertebrate animal, the brainless, skull- 
less Lancelet (Amphioxus). But in all other vertebrate 
animals, which we distinguish from the latter as skulled 
animals, or Craniota, a difference between the fore and 
hinder end of the marrow tube soon becomes visible, the 
fore end becoming dilated, and changing into a roundish 
bladder, the foundation of the brain. 

In all Craniota, that is, in all vertebrate animals possess- 
ing skull and brain, the brain, which is at first only the 
bladder-shaped dilatation of the anterior end of the spinal 
marrow, divides into five bladders lying one behind the 
other, four superficial, transverse in-nippings being formed. 
These five brain-bladders, out of which afterwards arise all 
the different parts of the intricately constructed brain, can 
be seen in their original condition in the embryo represented 
in Fig. 7. It is just the same whether we examine the em- 
bryo of a dog, a fowl, a lizard, or any other higher vertebrate 
animaL For the embryos of the different skulled animals 
(at least the three higher classes of them, the reptiles, birds 
and mammals) cannot be in any way distinguished at the 
stage represented in Fig. 7. The whole form of the body is 
as yet exceedingly simple, being merely a thin, leaf-like disc. 
Face, legs, intestines, etc., are as yet completely wanting. 
But the five bladders are already quite distinct from one 



Fig. 7. — Embryo of a mammal or bird, in 
which the live brain-bladders have just com. 
menced to develop, v. Fore brain, z. Twixt brain, 
m. Mid brain, h. Hind brain, n. After brain, 
p. Spinal-marrow, a. Eye-bladders, w. Primi- 
tive vertebrae, d. Spinal-axis or notochord. 

The first bladder, the fore brain (a), 
is in so far the most important that 
it principally forms the hemispheres of 
the so-called larger brain (cerebrum), 
that part which is the seat of the 
higher mental activities. The more 
these activities are developed in the 
series of vertebrate animals, the more 
do the two lateral halves of the fore 
brain, or the hemispheres, grow at the 
expense of the other bladders, and 
overlap them in front and from above. In man, where they 
are most strongly developed, agreeing with his higher men- 
tal activity, they eventually almost entirely cover the other 
parts from above (compare Plates II. and III.) The second 
bladder, the twixt brain (z), forms that portion of the 
brain which is called the centre of sight, and stands in 
the closest relation to the eyes (a), which grow right and 
left out of the fore brain in the shape of two bladders, and 
later lie at the bottom of the twixt brain. The third bladder, 
the mid brain (m), for the most part vanishes in the 
formation of the so-called four bulbs, a bossy portion of 
the brain, which is strongly developed in reptiles and 
birds (Fig. E, F, Plate II.), whereas in mammals it recedes 


much more (Fig. G, H, Plate III.). The fourth bladder, the 
hind brain Qi), forms the so-called little hemispheres, to- 
gether with the middle part of the small brain (cerebellum), 
a part of the brain as to the function of which the most con- 
tradictory conjectures are entertained, but which seems prin- 
cipally to regulate the co-ordination of movements. Lastly, 
the fifth bladder, the after brain (n), develops into that 
very important part of the central nervous system which 
is called the prolonged marrow (medulla oblongata). It 
is the central organ of the respiratory movements, and of 
other important functions, and an inj ury to it immediately 
causes death, whereas the large hemispheres of the fore brain 
(or the organ of the " soul," in a restricted sense) can be re- 
moved bit by bit, and even completely destroyed, without 
causing the death of the vertebrate animal — only its higher 
mental activities disappearing in consequence. 

These five brain bladders, in all vertebrate animals which 
possess a brain at all, are originally arranged in the same 
manner and develop gradually in the different groups so 
differently, that it is afterwards very difficult to recognize 
the corresponding parts in the fully-developed brains. In 
the early stage of development which is represented in 
Fig. 7, it seems as yet quite impossible to distinguish the 
embryos of the different mammals, birds, and reptiles, from 
one another. But if we compare the much more developed 
embryos on Plates II. and III. with one another, we can 
clearly see an inequality in their development, and especi- 
ally it will be perceived that the brain of the two mammals 
(G and H) already strongly differ from that of birds (F) and of 
reptiles (E). In the two latter the mid brain predominates, 
but in the former the fore brain. Even at this stage the 
VOL. I. x 


brain of the bird (F) is scarcely distinguishable from that of 
the tortoise (E), and in like manner the brain of the dog (G) 
is as yet almost the same as that of man (17). If, on the 
other hand, we compare the brains of these four vertebrate 
animals in a fully developed condition, we find them so 
very different in all anatomical particulars, that we cannot 
doubt for a moment as to which animal each brain belongs. 

I have here explained the original equality, the gradual 
commencement, and the ever increasing separation or 
differentiation of the embryos in the different vertebrate 
animals, taking the brain as a special example, just because 
this organ of the soul's activity is of special interest. But I 
might as well have discussed in its stead the heart, or the 
liver, or the limbs, in short, any other part of the body, since 
the same wonder of creation is here ever repeated, namely, 
this, that all parts are originally the same in the different 
vertebrate animals, and that the variations by which the 
different classes, orders, families, genera, etc., differ and 
deviate from one another, are only gradually developed. 

There are certainly few parts of the body which are so 
differently constructed as the limbs or extremities of the 
vertebrate animals. Now, I wish the reader to compare in 
Fig. A — if on Plates II. and III., the four extremities (bv) of 
the embryos with one another, and he will scarcely be able 
to perceive any important differences between the human 
arm (17 bv), the wing of a bird (F bv), the slim foreleg of a 
dog (Obv), and the plump foreleg of the tortoise (E bv). In 
comparing the hinder extremities (b h) in these figures he 
■will find it equally difficult to distinguish the leg of a man 
(Hbh), of a bird (Fbh), the hind-leg of a dog (Gbh), and 
that of a tortoise (Ebh). The fore as well as the hinder 


Germs or Embryos 

v. Fore -train , z. Twixt -train, m. Mid- Dram, h. Hind-train. , 

of four Vertebrates 


r • rik \hk a VL 


S3 \ i* <1 



na.Nose, a.Eyes, a Ear, k k k., s. Tail, 


extremities are as yet short, broad lumps, at the ends of 
which the foundations of the five toes are placed, connected 
as yet by a membrane. At a still earlier stage (Fig. A — D) 
the five toes are not marked out at all, and it is quite im- 
possible to distinguish even the fore and hinder extremities 
from one another. The latter, as well as the former, are 
nothing but simple roundish processes, which have grown 
out of the side of the trunk. At the very early stage 
represented in Fig. 7 they are completely wanting, and the 
whole embryo is a simple trunk without a trace of limbs. 

I wish especially to draw attention in Plates II. and 
III., which represents embryos in early stages of develop- 
ment (Fig. A — D) — and in which we are not able to recog- 
nize a trace of the full-grown animal — to an exceedingly 
important formation, which originally is common to all 
vertebrate animals, but which at a later period is trans- 
formed into the most different organs. Every one surely 
knows the gill-arches of fish, those arched bones which 
lie behind one another, to the number of three or four, 
on each side of the neck, and which support the gills, 
the respiratory organs of the fish (double rows of red leaves, 
which are popularly called " fishes' ears.") Now, these gill- 
arches originally exist exactly the same in man (D), in dogs 
(C), in fowls (B), and in tortoises (A), as well as in all other 
vertebrate animals. (In Fig. A — D the three gill-arches of 
the right side of the neck are marked k x k. 2 k 3 ). Now, it 
is only in fishes that these remain in their original form, and 
develop into respiratory organs. In the other vertebrate 
animals they are partly employed in the formation of the 
face (especially the jaw apparatus), and partly in the forma- 
tion of the organ of hearing. 


Finally, when comparing the emhryos on Plates II. and III., 
we must not fail to give attention again to the human 
tail (s), an organ which, in the original condition, man 
shares with all other vertebrate animals. The discovery of 
tailed men was long anxiously expected by many monistic 
philosophers, in order to establish a closer relationship 
between man and the other mammals. And in like manner 
their dualistic opponents often maintained with pride that 
the complete want of a tail formed one of the most important 
bodily distinctions between men and animals, though they 
did not bear in mind the many tailless animals which really 
exist. Now, man in the first months of development pos- 
sesses a real tail as well as his nearest kindred, the tailless 
apes (orang-outang, chimpanzee, gorilla), and vertebrate 
animals in general. But whereas, in most of them — for 
example, the dog (C, G) — in the course of development it 
always grows longer, in man (Fig. D, H) and in tailless 
mammals, at a certain period of development, it degenerates 
and finally completely disappears. However, even in fully 
developed men, the remnant of the tail is seen in the three, 
four, or five tail vertebrae (vertebra? coccygese) as an 
aborted or rudimentary organ, which forms the hinder or 
lower end of the vertebral column (p. 289). 

Most persons even now refuse to acknowledge the most 
important deduction of the Theory of Descent, that is, the 
palseontological development of man from ape-like, and 
through them from still lower, mammals, and consider such 
a transformation of organic form as impossible. But, I 
ask, are the phenomena of the individual development of 
man, the fundamental features of which I have here given, 
in any way less wonderful ? Is it not in the highest 


degree remarkable that all vertebrate animals of the most 
different classes — fishes, amphibious animals, reptiles, birds, 
and mammals — in the first periods of their embryonic 
development cannot be distinguished at all, and even much 
later, at a time when reptiles and birds are already distinctly 
different from mammals, that the dog and the man are 
almost identical ? Verily, if we compare those two series of 
development with one another, and ask ourselves which of 
the two is the more wonderful, it must be confessed that 
ontogeny, or the short and quick history of development of 
the individual, is much more mysterious than phylogeny, or 
the long and slow history of development of the tribe. For 
one and the same grand change of form is accomplished by 
the latter in the course of many thousands of years, and by 
the former in the course of a few months. Evidently this 
most rapid and astonishing transformation of the individual 
in ontogenesis, which we can actually point out at any 
moment by direct observation, is in itself much more 
wonderful and astonishing than the corresponding, but 
much slower and gradual transformation which the long 
chain of ancestors of the same individual has gone through 
in phylogenesis. 

The two series of organic development, the ontogenesis of 
the individual and the phylogenesis of the tribe to which 
it belongs, stand in the closest causal connection with each 
other. I have endeavoured, in the second volume of the 
" General Morphology," 4 to establish this theory in detail, 
as I consider it exceedingly important. As I have there 
shown, ontogenesis, or the development of the individual, is a 
short and quick repetition (recapitulation) of phylogenesis, 
or the development of the tribe to which it belongs, determined 


by the laws of inheritance and adaptation ; by tribe I 
mean the ancestors which form the chain of progenitors of 
the individual concerned. (Gen. Morph. ii. p. 110-147, 371.) 
In this intimate connection of ontogeny and phylogeny, I 
see one of the most important and irrefutable proofs of the 
Theory of Descent. No one can explain these phenomena 
unless he has recourse to the laws of Inheritance and 
Adaptation; by these alone are they explicable. These 
laws, which we have previously explained, are the laws of 
abbreviated, of homochronic, and of homotopic inheritance, 
and here deserve renewed consideration. As so high and 
complicated an organism as that of man, or the organism of 
every other mammal, rises upwards from a simple cellular 
state, and as it progresses in its differentiation and per- 
fecting it passes through the same series of transform- 
ations which its animal progenitors have passed through, 
during immense spaces of time, inconceivable ages ago. I 
have already pointed out this extremely important parallel- 
ism of the development of individuals and tribes (p. 10). 
Certain very early and low stages in the development of 
man, and the other vertebrate animals in general, correspond 
completely in many points of structure with conditions 
which last for life in the lower fishes. The next phase 
which follows upon this presents us with a change of the 
fish-like being into a kind of amphibious animal. At a later 
period the mammal, with its special characteristics, de- 
velops out of the amphibian, and we can clearly see, in the 
successive stages of its later development, a series of steps of 
progressive transformation which evidently correspond with 
the differences of different mammalian orders and families. 
Now, it is precisely in the same succession that we also see 


the ancestors of man, and of the higher mammals, appear 
one after the other in the earth's history ; first fishes, then 
amphibians, later the lower, and at last the higher mam- 
mals. Here, therefore, the embryonic development of 
the individual is completely parallel to the palseontological 
development of the whole tribe to which it belongs, and this 
exceedingly interesting and important phenomenon can be 
explained only by the interaction of the laws of Inheritance 
and Adaptation. 

The example last mentioned, of the parallelism of the 
palseontological and of the individual developmental series, 
now directs our attention to a third developmental series, 
which stands in the closest relations to these two, and which 
likewise runs, on the whole, parallel to them. I mean that 
series of development of forms which constitutes the object 
of investigation in comparative anatomy, and which I will 
briefly call the systematic developmental series of species. 
By this we understand the chain of the different, but re- 
lated and connected forms, which exist side by side at any 
one period of the earth's history ; as for example, at the 
present moment. While comparative anatomy compares the 
different forms of fully-developed organisms with one 
another, it endeavours to discover the common prototypes 
which underlie, as it were, the manifold forms of kindred 
genera, classes, etc., and which are more or less concealed by 
their particular differentiation. It endeavours to make out 
the series of progressive steps which are indicated in the 
different degrees of perfection of the divergent branches of 
the tribe. To make use again of the same particular in- 
stance, comparative anatomy shows us how the individual 
organs and systems of organs in the tribe of vertebrate 


animals — in the different classes, families, and species of it 
— have unequally developed, differentiated, and perfected 
themselves. It shows us how far the succession of classes 
of vertebrate animals, from the Fishes upwards, through the 
Amphibia to the Mammals, and here again, from the 
lower to the higher orders of Mammals, forms a progressive 
series or ladder. This attempt to establish a connected 
anatomical developmental series we may discover in the 
works of the great comparative anatomists of all ages — 
in the works of Goethe, Meckel, Cuvier, Johannes Muller, 
Gegenbaur, and Huxley. 

The developmental series of mature forms, which com- 
parative anatomy points out in the different diverging and 
ascending steps of the organic system, and which we call 
the systematic developmental series, is parallel to the 
palseontological developmental series, because it deals with 
the result of palEeontolgical development, and it is parallel 
to the individual developmental series, because this is 
parallel to the palaeontological series. If two parallels are 
parallel to a third, they must be parallel to one another. 

The varied differentiation, and the unequal degree of per- 
fecting which comparative anatomy points out in the 
developmental series of the System, is chiefly determined 
by the ever increasing variety of conditions of existence to 
which the different groups adapt themselves in the struggle 
for life, and by the different degrees of rapidity and com- 
pleteness with which this adaptation has been effected. 
Conservative groups which have retained their inherited 
peculiarities most tenaciously remain, in consequence, at the 
lowest and rudest stage of development. Those groups pro- 
gressing most rapidly and variously, and which have adapted 


themselves to changed conditions of existence most readily 
have attained the highest degree of perfection. The 
further the organic world developed in the course of the 
earth's history, the greater must the gap between the lower 
conservative and the higher progressive groups have be- 
come, as in fact may be seen too in the history of nations 
In this way also is explained the historical fact, that the 
most perfect animal and vegetable groups have developed 
themselves in a comparatively short time to a considerable 
height, while the lowest or most conservative groups have 
remained stationary throughout all ages in their original 
simple stage, or have progressed, but very slowly and 
gradually. The series of man's progenitors clearly shows 
this state of things. The sharks of the present day are still 
very like the primary fish, which are among the most 
ancient vertebrate progenitors of man, and the lowest 
amphibians of the present day (the gilled salamanders and 
salamanders) are very like the amphibians which first de- 
veloped themselves out of fishes. So, too, the later ances- 
tors of man, the Monotremata and Marsupials, the most 
ancient mammals, are at the same time the most imperfect 
animals of the class which still exist. 

The laws of inheritance and adaptation known to us are 
completely sufficient to explain this exceedingly important 
and interesting phenomenon, which may be briefly desig- 
nated as the parallelism of individual, of palo3ontological, 
and of systematic development. No opponent of the Theory 
of Descent has been able to give an explanation of this ex- 
tremely wonderful fact, whereas it is perfectly explained, 
according to the Theory of Descent, by the laws of Inherit- 
ance and Adaptation. 


If we examine this parallelism of the three organic 
series of development more accurately, we have to add 
the following special qualifications. Ontogeny, or the 
history of the individual development of every organism 
(embryology and metamorphology), presents us with a 
simple unbranching or graduated chain of forms ; and so it 
is with that portion of phytogeny which comprises the 
palseontological history of development of the direct ancestors 
only of an individual organism. But the whole of phylogeny 
— which meets us in the natural system of every organic 
tribe or phylum, and which is concerned with the investi- 
gation of the palseontological development of all the 
branches of this tribe — forms a branching or tree-shaped 
developmental series, a veritable pedigree. If we examine 
and compare the branches of this pedigree, and place them 
together according to the degree of their differentiation and 
perfection, we obtain the tree-shaped, branching, systematic 
developmental series of comparative anatomy. Strictly 
speaking, therefore, the latter is parallel to the whole of 
phylogeny, and consequently is only partially parallel to 
ontogeny ; for ontogeny itself is parallel only to a portion 
of phylogeny. 

All the phenomena of organic development above dis- 
cussed, especially the threefold genealogical parallelism, 
and the laws of differentiation and progress, which are 
evident in each of these three series of organic development, 
and, further, the whole history of rudimentary organs, are 
exceedingly important proofs of the truth of the Theory of 
Descent. For by it alone can they be explained, whereas 
its opponents cannot even offer a shadow of an explanation 
of them. Without the Doctrine of Filiation, the fact of 


organic development in general cannot be understood. We 
should therefore, for this reason alone, be forced to accept 
Lamarck's Theory of Descent, even if we did not possess 
Darwin's Theory of Selection. 




History of the Development of the Earth. — Kant's Theory of the Develop- 
ment of the Universe, or the Cosmological Gas Theory. — Development 
of Suns, Planets, and Moons. — First Origin of Water. — Comparison 
of Organisms and Anorgana. — Organic and Inorganic Substances. — 
Degrees of Density, or Conditions of Aggregation. — Albuminous 
Combinations of Carbon. — Organic and Inorganic Forms. — Crystals 
and Formless Organisms without Organs. — Stereometrical Fundamental 
Forms of Crystals and of Organisms. — Organic and Inorganic Forces. 
— Vital Force. — Growth and Adaptation in Crystals and in Organisms. 
— Formative Tendencies of Crystals. — Unity of Organic and In. 
organic Nature. — Spontaneous Generation, or Archigony. — Autogony 
and Plasmogony. — Origin of Monera by Spontaneous Generation. — 
Origin of Cells from Monera.— The Cell Theory.— The Plastid Theory. 
— Plastids, or Structural-Units. — Cytods and Cells. — Four Different 
Kinds of Plastids. 

In our considerations hitherto we have endeavoured to 
answer the question, " By what causes have new species of 
animals and plants arisen out of existing species ?" We 
have answered this question according to Darwin's theory, 
that natural selection in the struggle for existence — that is, 
the interaction of the laws of Inheritance and Adaptation 
— is completely sufficient for producing mechanically the 


endless variety of the different animals and plants, which 
have the appearance of being organized according to a plan 
for a definite purpose. Meanwhile the question must have 
already repeatedly presented itself to the reader, how did 
the first organisms, or that one original and primaeval organ- 
ism arise, from which we derive all the others ? 

This question Lamarck 2 answered by the hypothesis 
of spontaneous generation, or archigony. But Darwin 
passes over and avoids this subject, as he expressly 
remarks that he has " nothing to do with the origin of 
the soul, nor with that of life itself." At the conclusion 
of his work he expresses himself more distinctly in the 
following words : — " I imagine that probably all organic 
beings which ever lived on this earth descended from 
some primitive form, which was first called into life by 
the Creator." Moreover, Darwin, for the consolation of 
those who see in the Theory of Descent the destruction of 
the whole "moral order of the universe," appeals to the 
celebrated author and divine who wrote to him, that 
" he has gradually learnt to see that it is just as noble a 
conception of the Deity to believe that he created a few 
original forms capable of self-development into other and 
needful forms, as to believe that he required a fresh act 
of creation to supply the voids caused by the action of his 

Those to whom the belief in a supernatural creation is an 
emotional necessity may rest satisfied with this conception. 
They may reconcile that belief with the Theory of Descent ; 
for in the creation of a single original organism possessing 
the capability to develop all others out of itself by inherit- 
ance and adaptation, they can really find much more cause 


for admiring the power and wisdom of the Creator than in 
the independent creation of different species. 

If, taking this point of view, we were to explain the 
origin of the first terrestrial organisms, from which all the 
others are descended, as due to the action of a personal 
Creator acting according to a definite plan, we should of 
course have to renounce all scientific knowledge of the 
process, and pass from the domain of true science to the 
completely distinct domain of poetical faith. By assuming 
a supernatural act of creation we should be taking a leap 
into the inconceivable. Before we decide upon this latter 
step, and thereby renounce all pretension to a scientific 
knowledge of the process,- we are at all events in duty 
bound to endeavour to examine it in the light of a mechani- 
cal hypothesis. We must at least examine whether this 
process is really so wonderful, and whether we cannot form 
a tenable conception of a completely non-miraculous origin 
of the first primary organism. We might then be able 
entirely to reject miracle in creation. 

It will be necessary for this purpose, first of all, to go 
back further into the past, and to examine the history of 
the creation of the earth. Going back still further, we 
shall find it necessary to consider the history of the crea- 
tion of the whole universe in its most general outlines. 
All my readers undoubtedly know that from the struc- 
ture of the earth, as it is at present known to us, the 
notion has been derived, and as yet has not been refuted, 
that its interior is in a fiery fluid condition, and that the 
firm crust, composed of different strata, on the surface 
of which organisms are living, forms only a very thin 
pellicle or shell round the fiery fluid centre. We have 


arrived at this idea by different confirmatory experi- 
ments and reasonings. In the first place, the observation 
that the temperature of the earth's crust continually increases 
towards the centre is in favour of this supposition. The 
deeper we descend, the greater the warmth of the ground, 
and in such proportion, that with every 100 feet the 
temperature increases about one degree. At a depth of 
six miles, therefore, a heat of 1500° would be attained, suffi- 
cient to keep most of the firm substances of our earth's crust 
in a molten, fiery, fluid state. This depth, however, is only 
the 286th part of the whole diameter of the earth (1717 
miles). We further know that springs which rise out of a 
considerable depth possess a very high temperature, and 
sometimes even throw water up to the surface in a boiling 
state. Lastly, very important proofs are furnished by 
volcanic phenomena, the eruption of fiery fluid masses of 
stone bursting through certain parts of the earth's crust. 
All these phenomena lead us with great certainty to the im- 
portant assumption that the firm crust of the earth forms 
only quite a small fraction, not nearly the one-thousandth 
part of the whole diameter of the terrestrial globe, and that 
the rest is still for the most part in a molten or fiery 
fluid state. 

Now if, starting with this assumption, we reflect on the 
ancient history of the development of the globe, we are 
logically carried back a step further, namely, to the assump- 
tion that at an earlier date the whole earth was a fiery fluid 
body, and that the formation of a thin, stiffened crust on the 
surface was only a later process. Only gradually, by 
radiating its intrinsic heat into the cold space of the universe, 
has the surface of the glowing ball become condensed into 


a thin crust. That the temperature of the earth in remote 
times was much higher than it is now, is proved by 
many phenomena. Among other things, this is rendered 
probable by the equal distribution of organisms in remote 
times of the earth's history. While at present, as is well 
known, the different populations of animals and plants 
correspond to the different zones of the earth and their 
appropriate temperature, in earlier times this was distinctly 
not the case. 

We see from the distribution of fossils in the remoter 
ages, that it was only at a very late date, in fact, at a com- 
paratively recent period of the organic history of the 
earth (at the beginning of the so-called csenolithic or tertiary 
period), that a separation of zones and of the corresponding 
organic populations occurred. During the immensely long 
primary and secondary periods, tropical plants, which 
require a very high degree of temperature, lived not only 
in the present torrid zone, under the equator, but also in 
the present temperate and frigid zones. Many other 
phenomena also demonstrate a gradual decrease of the tem- 
perature of the globe as a whole, and especially a late and 
gradual cooling of the earth's crust about the poles. Bronn, 
in his excellent " Investigations of the Laws of Development 
of the Organic World," has collected numerous geological and 
palseontological proofs of this fact. 

These phenomena and the mathematico-astronomical know- 
ledge of the structure of the universe justify the theory that, 
inconceivable ages ago, long before the first existence of 
organisms, the whole earth was a fiery fluid globe. Now, this 
theory corresponds with the grand theory of the origin of 
the universe, and especially of our planetary system, which, 


on the ground of mathematical and astronomical facts, was 
put forward in 1755 by our critical philosopher Kant, 22 
and was later more thoroughly established by the celebrated 
mathematicians, Laplace and Herschel. This cosmogeny, or 
theory of the development of the universe, is now almost 
universally acknowledged ; it has not been replaced by a 
better one, and mathematicians, astronomers, and geologists 
have continually, by various arguments, strengthened its 

Kant's cosmogeny maintains that the whole universe, in- 
conceivable ages ago, consisted of a gaseous chaos. All the 
substances which are found at present separated on the 
earth, and other bodies of the universe, in different con- 
ditions of density — in the solid, semi-fluid, liquid, and elastic 
fluid or gaseous states of aggregation — originally constituted 
together one single homogeneous mass, equally filling up the 
space of the universe, which, in consequence of an extremely 
high degree of temperature, was in an exceedingly thin 
gaseous or nebulous state. The millions of bodies in 
the universe which at present form the different solar 
systems did not then exist. They originated only in con- 
sequence of a universal rotatory movement, or rotation, 
during which a number of masses acquired greater density 
than the remaining gaseous mass, and then acted upon the 
latter as central points of attraction. Thus arose a separa- 
tion of the chaotic primary nebula, or gaseous universe, into 
a number of rotating nebulous spheres, which became 
more and more condensed. Our solar system was such a 
gigantic gaseous or nebulous ball, all the particles of which 
revolved round a common central point, the solar nucleus. 
The nebulous ball itself, like all the rest, in consequence 



of its rotatory movement, assumed a spheroidal or a flattened 
globular form. 

While the centripetal force attracted the rotating particles 
nearer and nearer to the firm eentral point of the nebulous 
ball, and thus condensed the latter more and more, the cen- 
trifugal force, on the other hand, always tended to separate 
the peripheral particles further and further from it, and to 
hurl them off On the equatorial sides of the ball, which 
was flattened at both poles, this centrifugal force was 
strongest, and as soon as, by increase of density, it attained 
predominance over the centripetal force, a circular nebulous 
ring separated itself from the rotating balL This nebulous 
ring marked the course of future planets. The nebulous 
mass of the ring gradually condensed, and became a planet, 
which revolved round its own axis, and at the same 
time rotated round the central body. In precisely the 
same manner, from the equator of the planetary mass, as 
soon as the centrifugal force gained predominance over 
the centripetal force, new nebulous rings were ejected, 
which moved round the planets as the latter moved round 
the sun. These nebulous rings, too, became condensed into 
rotating balls. Thus arose the moons, only one of which 
moves round our earth, whilst four move round Jupiter, and 
six round Uranus. The ring of Saturn still shows us a moon 
in its early stage of development. As by increasing refrigera- 
tion these simple processes of condensation and expulson 
repeated themselves over and over again, there arose the 
different solar systems, the planets rotating round their 
central suns, and the satellites or moons moving round their 

The original gaseous condition of the rotating bodies of 


the universe gradually changed, by increasing refrigeration 
and condensation, into the fiery fluid or molten state of 
aggregation. By the process of condensation, a great 
quantity of heat wa3 emitted, and the rotating suns, planets, 
and moons, soon changed into glowing balls of fire, like 
gigantic drops of melted metal, which emitted light and 
heat. By loss of heat, the melted mass on the surface of the 
fiery fluid ball became further condensed, and thus arose a 
thin, firm crust, which enclosed a fiery fluid nucleus. In all 
essential respects our mother earth probably did not differ 
from the other bodies of the universe. 

In view of the object of these pages, it will not be of 
especial interest to follow in detail the history of the natural 
creation of the universe, with its different solar and planet- 
ary systems, and to establish it mathematically by the dif- 
ferent astronomical and geological proofs. The outlines of it, 
which I have just mentioned, must be sufficient here, and 
for further details I refer to Kant's* " General History of 
Nature and Theory of the Heavens." ffl I will only add 
that this wonderful theory, which might be called the cosmo- 
logical gas theory, harmonizes with all the general series of 
phenomena at present known to us, and stands in no irre- 
concilable contradiction to any one of them. Moreover, it 
is purely mechanical or monistic, makes use exclusively of 
the inherent forces of eternal matter, and entirely excludes 
every supernatural process, every prearranged and conscious 
action of a personal Creator. Kant's Cosmological Gas 
Theory consequently occupies a similar supreme position in 
Anorganology, especially in Geology, and forms the crown 
of our knowledge in that department, in the same 

* " Allgemeiue Naturgeschichte nnd Theoric des Ilimmels '* 


way as Lamarck's Theory of Descent does in Biology, and 
especially in Anthropology. Both rest exclusively upon 
mechanical or unconscious causes (causae efficientes), in no 
case upon prearranged or conscious causes (causae finales). 
(Compare above, p. 100-106). Both therefore fulfil all the 
demands of a scientific theory, and consequently will remain 
generally acknowledged until they are replaced by better 

I will, however, not deny that Kant's grand cosmogeny 
has some weak points, which prevent our placing the same 
unconditional confidence in it as in Lamarck's Theory of 
Descent. The notion of an original gaseous chaos filling 
the whole universe presents great difficulties of various 
kinds. A great and unsolved difficulty lies in the fact that 
the Cosmological Gas Theory furnishes no starting-point at 
all in explanation of the first impulse which caused the 
rotary motion in the gas-filled universe. In seeking for 
such an impulse, we are involuntarily led to the mistaken 
questioning about a " first beginning." We can as little 
imagine a first beginning of the eternal phenomena of the 
motion of the universe as of its final end. 

The universe is unlimited and immeasurable in both 
space and time. It is eternal, and it is infinite. Nor can 
we imagine a beginning or end to the uninterrupted and 
eternal motion in which all particles of the universe are 
always engaged. The great laws of the conservation of 
force ^ and the conservation of matter, the foundations 
of our whole conception of nature, admit of no other supposi- 
tion. The universe, as far as it is cognisable to human 
capability, appears as a connected chain of material phe- 
nomena of motion, necessitating a continual change of 


forms. Every form, as the temporary result of a multi- 
plicity of phenomena of motion, is as such perishable, and 
of limited duration. But, in the continual change of forms, 
matter and the motion inseparable from it remain eternal 
and indestructible. 

Now, although Kant's Cosmological Gas Theory is not able 
to explain the development of motion in the whole universe 
in a satisfactory manner, beyond that gaseous state of chaos, 
and although many other weighty considerations may be 
brought forward against it, especially by chemistry 
and geology, yet we must on the whole acknowledge its 
great merit, inasmuch as it explains in an excellent 
manner, by due consideration of development, the whole 
structure of all that is accessible to our observation, that is, 
the anatomy of the solar systems, and especially of our 
planetary system. It may be that this development was 
altogether different from what Kant supposes, and our 
earth may have arisen by the aggregation of numberless 
small meteorides, scattered in space, or in any other manner, 
but hitherto no one has as yet been able to establish any 
other theory of development, or to offer one in the place 
of Kant's cosmogeny. 

After this general glance at the monistic cosmogeny, or 
the non-miraculous history of the development of the 
universe, let us now return to a minute fraction of it, to our 
mother earth, which we left as a ball flattened at both poles 
and in a fiery fluid state, its surface having condensed by 
becoming cooled into a very thin firm crust. The crust, on 
first cooling, must have covered the whole surface of the 
terrestrial sphere as a continuous smooth and thin shell. 
But soon it must have become uneven and hummocky ; for, 


since during the continued cooling, the fiery fluid nucleus 
became more and more condensed and contracted, and 
consequently the diameter of the earth diminished, the 
thin cold crust, which could not closely follow the softer 
nuclear mass, must have fallen in, in many places. An 
empty space would have arisen between the two, had not 
the pressure of the outer atmosphere forced down the 
fragile crust towards the interior, breaking it in so doing. 
Other unevennesses probably arose from the fact that, in 
different parts, the cooled crust during the process of 
refrigeration contracted also itself, and thus became fissured 
with cracks and rents. The fiery fluid nucleus flowed up 
to the external surface through these cracks, and again 
became cooled and stiff. Thus, even at an early period there 
arose many elevations and depressions, which were the first 
foundations of mountains and valleys. 

After the temperature of the cooled terrestrial ball had 
fallen to a certain degree, a very important new process was 
effected, namely, the first origin of water. "Water had until 
then existed only in the form of steam in the atmosphere 
surrounding the globe. The water could evidently not con- 
dense into a state of fluid drops until the temperature of the 
atmosphere had considerably decreased. Now, then, there 
began a further transformation of the earth's crust by the force 
of water. It continually fell in the form of rain, and in that 
form washed down the elevations of the earth's crust, 
filling the depressions with the mud carried along, and, by 
depositing it in layers, it caused the extremely important 
neptunic transformations of the earth's crust, which have 
continued since then uninterruptedly, and which in our 
next chapter we shall examine a little more closely. 


It was not till the earth's crust had so far cooled that the 
water had condensed into a fluid form, it was not till the 
hitherto dry crust of the earth had for the first time become 
covered with liquid water, that the origin of the first 
organisms could take place. For all animals and all plants — 
in fact, all organisms — consist in great measure of fluid 
water, which combines in a peculiar manner with other sub- 
stances, and brings them into a semi-fluid state of aggrega- 
tion We can therefore, from these general outlines of the 
inorganic history of the earth's crust, deduce the important 
fact, that at a certain definite time life had its beginning on 
earth, and that terrestrial organisms did not exist from 
eternity, but at a certain period came into existence for the 
first time. 

Now, how are we to conceive of this origin of the first 
organisms ? This is the point at which most naturalists, 
even at the present day, are inclined to give up the attempt 
at natural explanation, and take refuge in the miracle of an 
inconceivable creation. In doing so, as has already been re- 
marked, they quit the domain of scientific knowledge, and 
renounce all further insight into the eternal laws which have 
determined nature's history. But before despondingly taking 
such a step, and before we despair of the possibility of 
any knowledge of this important process, we may at least 
make an attempt to understand it. Let us see if in reality 
the origin of a first organism out of inorganic matter, the 
origin of a living body out of lifeless matter, is so utterly 
inconceivable and beyond all experience. In one word, let 
us examine the question of spontaneous generation, or archi- 
gony. In so doing, it is above all things necessary to form 
a clear idea of the principal properties of the two chief 


groups of natural bodies, the so-called inanimate or inor- 
ganic, and the animate or organic bodies, and then estab- 
lish what is common to, and what are the differences be- 
tween, the two groups. It is desirable to go somewhat care- 
fully into the comparison of organisms and anorgana, 
since it is commonly very much neglected, although it is 
necessary for a right understanding of nature from the 
monistic point of view. It will be most advantageous here 
to look separately at the three fundamental properties of 
every natural body ; these are matter, form, and force. Let 
usjbegin with matter. (Gen. Morph. iii.) 

By chemistry we have succeeded in analysing all bodies 
known to us into a small number of elements or simple sub- 
stances, which cannot be further divided, for example, 
carbon, oxygen, nitrogen, sulphur, and the different metals : 
potassium, sodium, iron, gold, etc. At present we know 
about seventy such elements or simple substances. The 
majority of them are unimportant and rare ; the minority 
only are widely distributed, and compose not only most of 
the anorgana, but also all organisms. If we compare those 
elements which constitute the body of organisms with those 
which are met with in anorgana, we have first to note the 
highly important fact that in animal and vegetable bodies 
no element occurs but what can be found outside of them in 
inanimate nature. There are no special organic elements or 
simple organic substances. 

The chemical and physical differences existing between 
organisms and anorgana, consequently, do not lie in their 
material foundation; they do not arise from the different 
nature of the elements composing them, but from the dif- 
ferent manner in which the latter are united by chemical 


combination. This different manner of combination gives 
rise to certain physical peculiarities, especially in density of 
substance, which at first sight seems to constitute a deep 
chasm between the two groups of bodies. Inorganic or 
inanimate natural bodies, such as crystals and the amorphous 
rocks, are in a state of density which we call the firm or 
solid state, and which we oppose to the liquid state of water 
and to the gaseous state of air. It is familiar to every one 
that these three different degrees of density, or states of 
aggregation of anorgana, are by no means peculiar to the 
different elements, but are the results of a certain degree 
of temperature. Every inorganic solid body, by increase of 
temperature, can be reduced to the liquid or melted state, 
and, by further heat, to the gaseous or elastic state. In the 
same way most gaseous bodies, by a proper decrease of 
temperature can first be converted into a liquid state, and 
further, into a solid state of density. 

In opposition to these three states of density of anorgana, 
the living body of all organisms — animals as well as plants 
— is in an altogether peculiar fourth state of aggregation. 
It is neither solid like stone, nor liquid like water, but pre- 
sents rather a medium between these two states, which may 
therefore be designated as the firm-fluid or swollen state of 
aggregation (viscid). In all living bodies, without exception, 
there is a certain quantity of water combined in a peculiar 
way with solid matter, and owing to this characteristic 
combination of water with solid matter we have that 
soft state of aggregation, neither solid nor liquid, which 
is of great importance in the mechanical explanation of 
the phenomena of life. Its cause lies essentially in the 
physical and chemical properties of a simple, indivisible, 


elementary substance, namely, carbon (Gen. Morph. i. 

Of all elements, carbon is to us by far the most important 
and interesting, because this simple substance plays the 
largest part in all animal and vegetable bodies known to 
us. It is that element which, by its peculiar tendency to 
form complicated combinations with the other elements, 
produces the greatest variety of chemical compounds, and 
among them the forms and living substance of animal and 
vegetable bodies. Carbon is especially distinguished by 
the fact that it can unite with the other elements in 
infinitely manifold relations of number and weight. By the 
combination of carbon with three other elements, with 
oxygen, hydrogen, and nitrogen (to which generally sulphur, 
and frequently, also, phosphorus is added), there arise those 
exceedingly important compounds which we have become 
acquainted with as the first and most indispensable 
substratum of all vital phenomena, the albuminous combina- 
tions, or albuminous bodies (protean matter). 

We have before this (p. 185) become acquainted with the 
simplest of all species of organisms in the Monera, whose 
entire bodies when completely developed consist of nothing 
but a semi-fluid albuminous lump ; they are organisms which 
are of the utmost importance for the theory of the first 
origin of life. But most other organisms, also, at a certain 
period of their existence — at least, in the first period of their 
life — in the shape of egg-cells or germ-cells, are essentially 
nothing but simple little lumps of such albuminous forma- 
tive matter, known as plasma, or protoplasma. They then 
differ from the Monera only by the fact that in the interior 
of the albuminous corpuscle the cell-kernel, or nucleus, has 


separated itself from the surrounding cell-substance (proto- 
plasma). As we have already pointed out, the cells, with 
their simple attributes, are so many citizens, who by 
co-operation and differentiation build up the body of even 
the most perfect organism ; this being, as it were, a cell 
republic (p. 301). The fully developed form and the vital 
phenomena of such an organism are determined solely by the 
activities of these small albuminous corpuscles. 

It may be considered as one of the greatest triumphs of 
recent biology, especially of the theory of tissues, that we 
are now able to trace the wonder of the phenomena of life 
to these substances, and that we can demonstrate the 
infinitely manifold and complicated physical and chemical 
properties of the albuminous bodies to be the real cause of 
organic or vital phenomena. All the different forms of 
organisms are simply and directly the result of the combi- 
nation of the different forms of cells. The infinitely 
manifold varieties of form, size, and combination of the cells 
have arisen only gradually by the division of labour, and by 
the gradual adaptation of the simple homogeneous lumps of 
plasma, which originally were the only constituents of the 
cell-mass. From this it follows of necessity that the 
fundamental phenomena of life — nutrition and generation — 
in their highest manifestations, as well as in their simplest 
expressions, must also be traced to the material nature of 
that albuminous formative substance. The other vital 
activities are gradually evolved from these two. Thus, 
then, the general explanation of life is now no more 
difficult to us than the explanation of the physical properties 
of inorganic bodies. All vital phenomena and formative 
processes of organisms are as directly dependent upon the 


chemical composition and the physical forces of organic 
matter as the vital phenomena of inorganic crystals — that is, 
the process of their growth and their specific formation — are 
the direct results of their chemical composition and of their 
physical condition. The ultimate causes, it is true, remain 
in both cases concealed from us. When gold and copper 
crystallize in a cubical, bismuth and antimony in a 
hexagonal, iodine and sulphur in a rhombic form of 
crystal, the occurrence is in reality neither more nor less 
mysterious to us than is every elementary process of 
organic formation, every self-formation of the organic cell. 
In this respect we can no longer draw a fundamental 
distinction between organisms and anorgana, a distinction 
of which, formerly, naturalists were generally convinced. 

Let us secondly examine the agreements and differences 
which are presented to us in the formation of organic and 
inorganic natural bodies (Gen. Morph. i. 130). Formerly 
the simple structure of the latter and the composite 
structure of the former were looked upon as the principal 
distinction. The body of all organisms was supposed to 
consist of dissimilar or heterogeneous parts, of instruments 
or organs which worked together for the purposes of life. 
On the other hand, the most perfect anorgana, that is to say, 
crystals, were supposed to consist entirely of continuous or 
homogeneous matter. This distinction appears very essen- 
tial. But it loses all importance through the fact that in 
late years we have become acquainted with the exceedingly 
remarkable and important Monera. 15 (Compare above, 
p. 185). The whole body of these most simple of all 
organisms — a semi-fluid, formless, and simple lump of 
albumen — consists, in fact, of only a single chemical combi- 


nation, and is as perfectly simple in its structure as any 
crystal, which consists of a single inorganic combination, 
for example, of a metallic salt or of a silicate of the earths 
and alkalies. 

As naturalists believed in differences in the inner struc- 
ture or composition, so they supposed themselves able to 
find complete differences in the external forms of organisms 
and anorgana, especially in the mathematically determinable 
crystalline forms of the latter. Certainly crystallization 
is pre-eminently a quality of the so-called anorgana. 
Crystals are limited by plane surfaces, which meet in 
straight lines and at certain measurable angles. Animal 
and vegetable forms, on the contrary, seem at first sight to 
admit of no such geometrical determination. They are for 
the most part limited by curved surfaces and crooked lines, 
which meet at variable angles. But in recent times we 
have become acquainted, among Radiolaria 23 and among 
many other Protista, with a large number of lower 
organisms, whose body, in the same way as crystals, may be 
traced to a mathematically determinable fundamental form, 
and whose form in its whole, as well as in its parts, is 
bounded by definite geometrically determinable planes and 
angles. In my general doctrine of Fundamental Forms, or 
Promorphology, I have given detailed proofs of this, and at 
the same time established a general system of forms, the ideal 
stereometrical type-forms, which explain the real forms of 
inorganic crystals, as well as of organic individuals (Gen. 
Morph. i. 375-574). Moreover, there are also perfectly 
amorphous organisms, like the Monera, Amoeba, etc., which 
change their forms every moment, and in which we are as 
little able to point out a definite fundamental form as in 


the case of the shapeless or amorphous anorgana, such as 
non-crystallized stones, deposits, etc. We are consequently 
unable to find any essential difference in the external 
forms or the inner structure of anorgana and organisms. 

Thirdly, let us turn to the forces or the jihenomena of 
motion of these two different groups of bodies (Gen. Morph. 
i. 140). Here we meet with the greatest difficulties. The 
vital phenomena, known as a rule only in the highly 
developed organisms, in the more perfect animals and plants, 
seem there so mysterious, so wonderful, so peculiar, that 
most persons are decidedly of opinion that in inorganic 
nature there occurs nothing at all similar, or in the least 
degree comparable to them. Organisms are for this very 
reason called animate, and the anorgana, inanimate natural 
bodies. Hence, even so late as the commencement of the 
present century, the science which investigates the 
phenomena of life, namely physiology, retained the 
erroneous idea that the physical and chemical properties 
of matter were not sufficient for explaining these 
phenomena. In our own day, especially during the last 
ten years, this idea may be regarded as having been com- 
pletely refuted. In physiology, at least, it has now no 
place. It now never occurs to a physiologist to consider 
any of the vital phenomena as the result of a mysterious 
vital force, of an active power working for a definite purpose, 
standing outside of matter, and, so to speak, taking only 
the physico-chemical forces into its service. Modern 
physiology has arrived at the strictly monistic conviction 
that all of the vital phenomena, and, above all, the two 
fundamental phenomena of nutrition and propagation are 
purely physico-chemical processes, and directly dependent 


on the material nature of the organism, just as all the 
physical and chemical qualities of every crystal are 
determined solely by its material composition. Now, as 
the elementary substance which determines the peculiar 
material composition of organisms is carbon, we must 
ultimately reduce all vital phenomena, and, above all, the 
two fundamental phenomena of nutrition and propagation 
to the properties of the carbon. The peculiar -chemico- 
physieal properties, and especially the semi-fluid state of 
aggregation, and the easy decomposibility of the exceedingly 
composite albuminous combinations of carbon, are the 
mechanical causes of those peculiar phenomena of motion 
which distinguish organisms from anorgana, and tuhich 
in a narrow sense are usually called " life." 

In order to understand this " carbon theory," which I have 
established in detail in the second book of my General 
Morphology, it is necessary, above all things, closely to 
examine those phenomena of motion which are common to 
both groups of natural bodies. First among them is the 
process of growth. If we cause any inorganic solution of 
salt slowly to evaporate, crystals are formed in it, which 
slowly increase in size during the continued evaporation of 
the water. This process of growth arises from the fact 
that new particles continually pass over from the fluid state 
of aggregation into the solid, and, according to certain laws, 
deposit themselves upon the firm kernel of the crystal 
already formed From such an apposition of particles arise 
the mathematically definite crystalline shapes. In like 
manner the growth of organisms takes place by the accession 
of new particles. The only difference is that in the growth 
of organisms, in consequence of their semi-fluid state of 


aggregation, the newly-added particles penetrate into the 
interior of the organism (inter-susception), whereas anor- 
gana receive homogeneous matter from without only by 
apposition or an addition of new particles to the surface. 
This important difference of growth by inter-susception 
and by apposition is obviously only the necessary and direct 
result of the different conditions of density or state of 
aggregation in organisms and anorgana. 

Unfortunately I cannot here follow in detail the various 
exceedingly interesting parallels and analogies which occur 
between the formation of the most perfect anorgana, the 
crystals, and the formation of the simplest organisms, the 
Monera and their next kindred forms. For this I must 
refer to a minute comparison of organisms and anorgana, 
which I have carried out in the fifth chapter of my General 
Morphology (Gen. Morph. i. 111-160). I have there 
shown in detail that there exist no complete differences 
between organic and inorganic natural bodies, neither in 
respect to form and structure, nor in respect to matter and 
force ; and that the actually existing differences are dependent 
upon the peculiar nature of the carbon; and that there 
exists no insurmountable chasm between organic and 
inorganic nature. We can perceive this most important 
fact very clearly if we examine and compare the origin of 
the forms in crystals and in the simplest organic individuals. 
In the formation of crystal individuals, two different counter- 
acting formative tendencies come into operation. The inner 
constructive force, or the inner formative tendency, which 
corresponds to the Heredity of organisms, in the case of the 
crystal is the direct result of its material constitution or of 
its chemical composition. The form of the crystal, so far as 


it is determined by this inner original formative tendency, 
is the result of the specific and definite way in which the 
smallest particles of the crystallizing matter unite together 
in different directions according to law. That independent 
inner formative force, which is directly inherent in the 
matter itself, is directly counteracted by a second formative 
force. The external constructive force, or the external 
formative tendency, may be called Adaptation in crystals as 
well as in organisms. Every crystal individual during its 
formation, like every organic individual, must submit and 
adapt itself to the surrounding influences and conditions 
of existence of the outer world In fact, the form and size of 
every crystal is dependent upon its whole surroundings, for 
example, upon the vessel in which the crystallization takes 
place, upon the temperature and the pressure of the air 
under which the crystal is formed, upon the presence or 
absence of heterogeneous bodies, etc. Consequently, the 
form of every single crystal, like the form of every single 
organism, is the result of the interaction of two opposing 
factors — the inner formative tendency, which is determined 
by the chemical constitution of the matter itself, and of the 
external formative tendency, which is dependent upon the 
influence of surrounding matter. Both these constructive 
forces interact similarly also in the organism, and, just as in 
the crystal, are of a purely mechanical nature and directly 
inherent in the substance of the body. If we designate the 
growth and the formation of organisms as a process of life, we 
may with equal reason apply the same term to the developing 
crystal. The teleological conception of nature, which looks 
upon organisms as machines of creation arranged for a 
definite purpose, must logically acknowledge the same also 
vol. I. z 


in regard to the forms of crystals. The differences which 
exist between the simplest organic individuals and inorganic 
crystals are determined by the solid state of aggregation of 
the latter, and by the semi-fluid state of the former. 
Beyond that the causes producing form are exactly the 
same in both. This conviction forces itself upon us most 
clearly, if we compare the exceedingly remarkable pheno- 
mena of growth, adaptation, and the " correlation of parts " 
of developing crystals with the corresponding phenomena 
of the origin of the simplest organic individuals (Monera 
and cells). The analogy between the two is so great that, 
in reality, no accurate boundary can be drawn. In my 
General Morphology I have quoted in support of this a 
number of striking facts (Gen. Morph. i. 146, 156, 158.) 

If we vividly picture to ourselves this "unity of 
organic and inorganic nature" this essential agreement of 
organisms and anorgana in matter, form, and force, and if 
we bear in mind that we are not able to establish any 
one fundamental distinction between these two groups of 
bodies (as was formerly generally assumed), then the ques- 
tion of spontaneous generation will lose a great deal of the 
difficulty which at first seems to surround it. Then the 
development of the first organism out of inorganic matter 
will appear a much more easily conceivable and intelligible 
process than has hitherto been the case, whilst an artificial 
absolute barrier between organic or animate, and inorganic 
or inanimate nature was maintained. 

In the question of spontaneous generation, or archigony, 
which we can now answer more definitely, it must be borne 
in mind that by this conception we understand generally 
the non-parental generation of an organic individual, the 


origin of an organism independent of a parental or pro- 
ducing organism. It is in this sense that on a former 
occasion (p. 183) I mentioned spontaneous generation 
(archigony) as opposed to parental generation or propaga- 
tion (tocogony). In the latter case the organic individual 
arises by a greater or less portion of an already existing 
organism separating itself and growing independently. 
(Gen Morph. ii. 32.) 

In spontaneous generation, which is often also called 
original generation (generatio spontanea, asquivoca, primaria 
etc,) we must first distinguish two essentially different 
kinds, namely, autogeny and plasmogeny. By autogeny 
we understand the origin of a most simple organic indi- 
vidual in an inorganic formative fluid, that is, in a 
fluid which contains the fundamental substances for the 
composition of the organism dissolved in simple and loose 
combinations (for example, carbonic acid, ammonia, binary 
salts, etc.). On the other hand, we call spontaneous genera- 
tion plasmogeny when the organism arises in an organic 
formative fluid, that is, in a fluid which contains those 
requisite fundamental substances dissolved in the form of 
complicated and fluid combinations of carbon (for example, 
albumen, fat, hydrate of carbon, etc.). (Gen. Morph. i. 174. 
ii. 33.) 

Neither the process of autogeny, nor that of plasmogeny, 
has yet been directly observed with perfect certainty. 
In early, and also in more recent times, numerous and 
interesting experiments have been made as to the possibility 
or reality of spontaneous generation. Almost all these 
experiments refer not to autogeny, but to plasmogeny, to the 
origin of an organism out of already formed organic matter. 


It is evident, however, that this latter process is only of 
subordinate interest for our history of creation. It is much 
more important for us to solve the question, " Is there such, 
a thing as autogeny ? Is it possible that an organism can 
arise, not out of pre-existing organic, but out of purely inor- 
ganic, matter ? " Hence we can quietly lay aside all the 
numerous experiments which refer only to plasmogeny, 
which have been carried on very zealously during the last 
ten years, and which for the most part have had a negative 
result. For even supposing that the reality of plasmogeny 
were strictly proved, still autogeny would not be explained 
by it. 

The experiments on autogeny have likewise as yet 
furnished no certain and positive result. Yet we must at 
the outset most distinctly protest against the notion 
that these experiments have proved the impossibility of 
spontaneous generation in general. Most naturalists who 
have endeavoured to decide this question experimentally, 
and who, after having employed all possible precautionary 
measures, under well-ascertained conditions, have seen no 
organisms come into being, have straightway made the 
assertion, on the ground of these negative results : " That it 
is altogether impossible for organisms to come into existence 
by themselves without parental generation" This hasty 
and inconsiderate assertion they have supported by the 
negative results of their experiments, which, after all, could 
prove nothing except that, under these or those highly 
artificial circumstances created by the experimenters them- 
selves, no organism was developed. From these experi- 
ments, which have been for the most part made under the 
most unnatural conditions, and in a highly artificial 


manner, we can by no means draw the conclusion that 
spontaneous generation in general is impossible. The 
impossibility of such a process can, in fact, never be proved. 
For how can we know that in remote primaeval times there 
did not exist conditions quite different from those at 
present obtaining, and which may have rendered spon- 
taneous generation possible ? Indeed, we can even positively 
and with full asssurance maintain that the general 
conditions of life in primaeval times must have been entirely 
different from those of the present time. Think only of the 
fact that the enormous masses of carbon which we now 
find deposited in the primary coal mountains were first 
reduced to a solid form by the action of vegetable fife, and 
are the compressed and condensed remains of innumerable 
vegetable substances, which have accumulated in the course 
of many millions of years. But at the time when, after 
the origin of water in a liquid state on the cooled 
crust of the earth, organisms were first formed by 
spontaneous generation, those immeasurable quantities of 
carbon existed in a totally different form, probably for the 
most part dispersed in the atmosphere in the shape of 
carbonic acid. The whole composition of the atmosphere 
was therefore extremely different from the present. 
Further, as may be inferred upon chemical, physical, and 
geological grounds, the density and the electrical conditions 
of the atmosphere were quite different. In like manner the 
chemical and physical nature of the primaeval ocean, which 
then continuously covered the whole surface of the earth as 
an uninterrupted watery sheet, was quite peculiar. The 
temperature, the density, the amount of salt, etc., must have 
been very different from those of the present ocean. In 


any case, therefore, even if we do not know anything more 
about it, there remains to us the supposition, which can at 
least not be disputed, that at that time, under conditions 
quite different from those of to-day, a spontaneous genera- 
tion, which now is perhaps no longer possible, may have 
taken place. 

But it is necessary to add here that, by the recent pro- 
gress of chemistry and physiology, the mysterious and 
miraculous character which at first seems to belong to this 
much disputed and yet inevitable process of spontaneous 
generation, has been to a great extent, or almost entirely, 
destroyed. Not fifty years ago, all chemists maintained that 
we were unable to produce artificially in our laboratories 
any complicated combination of carbon, or so-called "organic 
combination." The mystic " vital force " alone was sup- 
posed to be able to produce these combinations. When, 
therefore, in 1828, Wohler, in Gottingen, for the first time 
refuted this dogma, and exhibited pure " organic " urea, ob- 
tained in an artificial manner from a purely inorganic body 
(cyanate of ammonium), it caused the greatest surprise and 
astonishment. In more recent times, by the progress of syn- 
thetic chemistry, we have succeeded in producing in our 
laboratories a great variety of similar " organic " combin- 
ations of carbon, by purely artificial means — for example 
alcohol, acetic acid, formic acid. Indeed, many exceed- 
ingly complicated combinations of carbon are now arti- 
ficially produced, so that there is every likelihood, sooner 
or later, of our producing artificially the most complicated, 
and at the same time the most important of all, namely, the 
albuminous combinations, or plasma-bodies. By the con- 
sideration of this probability, the deep chasm which was 


formerly and generally believed to exist between organic 
and inorganic bodies is almost or entirely removed, and the 
way is paved for the conception of spontaneous generation. 

Of still greater, nay, the very greatest importance to the 
hypothesis of spontaneous generation are, finally, the exceed- 
ingly remarkable Monera, those creatures which we have 
already so frequently mentioned, and which are not only the 
simplest of all observed organisms, but even the simplest of 
all imaginable organisms. I have already described these 
wonderful " organisms without organs," when examining 
the simplest phenomena of propagation and inheritance. 
We already know seven different genera of these Monera, 
some of which live in fresh water, others in the sea (com- 
pare above, p. 184 ; also Plate I. and its explanation 
in the Appendix). In a perfectly developed and freely 
motile state, they one and all present us with nothing but a 
simple little lump of an albuminous combination of carbon. 
The individual genera and species differ only a little in the 
manner of propagation and development, and in the way of 
taking nourishment. Through the discovery of these organ- 
isms, which are of the utmost importance, the supposition 
of a spontaneous generation loses most of its difficulties. 
For as all trace of organization — all distinction of hetero- 
geneous parts — is still wanting in them, and as all the vital 
phenomena are performed by one and the same homogeneous 
and formless matter, we can easily imagine their origin by 
spontaneous generation. If this happens through plas- 
mogeny, and if plasma capable of life already exists, it 
then only needs to individualize itself in the same way as 
the mother liquor of crystals individualizes itself in crys- 
tallization. If, on the other hand, the spontaneous generation 


of the Monera takes place by true autogeny, then it is 
further requisite that that plasma capable of life, that pri- 
maeval mucus, should be formed out of simpler combinations 
of carbon. As we are now able artificially to produce, 
in our laboratories, combinations of carbon similar to this 
in the complexity of their constitution, there is absolutely 
no reason for supposing that there are not conditions in free 
nature also, in which such combinations could take place. 
Formerly, when the doctrine of spontaneous generation was 
advocated, it failed at once to obtain adherents on account 
of the composite structure of the simplest organisms then 
known. It is only since we have discovered the exceedingly 
important Monera, only since we have become acquainted 
in them with organisms not iu any way built up of distinct 
organs, but which consist solely of a single chemical combin- 
ation, and yet grow, nourish, and propagate themselves, that 
this great difficulty has been removed, and the hypothesis of 
spontaneous generation has gained a degree of probability 
which entitles it to fill up the gap existing between Kant's 
cosmogony and Lamarck's Theory of Descent. Even 
among the Monera at present known there is a species 
which probably, even now, always comes into existence by 
spontaneous generation. This is the wonderful Bathybius 
Hceckelii, discovered and described by Huxley. As I have 
already mentioned (p. 184), this Moneron is found in the 
greatest depths of the sea, at a depth of between 12,000 and 
24,000 feet, where it covers the ground partly as retiform 
threads and plaits of plasma, partly in the form of larger or 
smaller irregular lumps of the same material.* 

* We must wait for fuller information on the subject of Bathybius, at the 
hands of the naturalists of the Challenger expedition, before accepting 
it finally as a distinct organism. — Editor. 


Only such homogeneous organisms as are yet not 
differentiated, and are similar to inorganic crystals in 
being homogeneously composed of one single substance, 
could arise by spontaneous generation, and could become the 
primaeval parents of all other organisms. In their further 
development we have pointed out that the most important 
process is the formation of a kernel or nucleus in the simple 
little lump of albumen. We can conceive this to take place 
in a purely physical manner, by the condensation of the 
innermost central part of the albumen. The more solid 
central mass, which at first gradually shaded off into the 
peripheral plasma, becomes sharply separated from it, and 
thus forms an independent, round, albuminous corpuscle, 
the kernel ; and by this process the Moneron becomes 
a cell. Now, it must have become evident from our 
previous chapters, that the further development of all 
other organisms out of such a cell presents no difficulty, for 
every animal and every plant, in the beginning of its indi- 
vidual life, is a simple cell. Man, as well as every other 
animal, is at first nothing but a simple egg-cell, a single 
lump of mucus, containing a kernel (p. 297, Fig 5). 

In the same way as the kernel of the organic cell 
arose in the interior or central mass of the originally homo- 
geneous lump of plasma, by separation, so, too, the first cell- 
rnembrane was formed on its surface. This simple, but most 
important process, as has already been remarked, can like- 
wise be explained in a purely physical manner, either as a 
chemical deposit, or as a physical condensation in the upper- 
most stratum of the mass, or as a secretion. One of the first 
processes of adaptation effected by the Moneron originating 
by spontaneous generation must have been the condensation 


of an external crust, which as a protecting covering shut in 
the softer interior from the hostile influences of the 
outer world. As soon as, by condensation of the homo- 
geneous Moneron, a cell-kernel arose in the interior and 
a membrane arose on the surface, all the fundamental 
parts of the unit were furnished, out of which, by infinitely 
manifold repetition and combination, as attested by actual 
observation, the body of higher organisms is constructed. 

As has already been mentioned, our whole understanding 
of an organism rests upon the cell theory established thirty 
years ago by Schleiden and Schwann According to it, 
every organism is either a simple cell or a cell-community, 
a republic of closely connected cells. All the forms and 
vital phenomena of every organism are the collective result 
of the forms and vital phenomena of all the single cells of 
which it is composed. By the recent progress of the cell 
theory it has become necessary to give the elementary 
organisms, that is, the " organic " individuals of the first 
order, which are usually designated as cells, the more 
general and more suitable name of form-units, or plastids, 
Among these form-units we distinguish two main groups, 
namely, the cytods and the genuine cells. The cytods are, 
like the Monera, pieces of plasma without a kernel 
(p. 186, Fig. 1). Cells, on the other hand, are pieces of plasma 
containing a kernel or nucleus (p. 188, Fig. 2). Each of 
these two main groups of plastids is again divided into two 
subordinate groups, according as they possess or do not 
possess an external covering (skin, shell, or membrane). 
We may accordingly distinguish the following four grades 
or species of plastids, namely : 1. Simple cytods (p. 186, 
Fig. 1 A) ; 2. Encased cytods; 3. Simple cells (p. 188, 


Fig. 2 5); 4. Encased cells (p. 188, Fig. 2 A). (Gen. Morph. 
i. 269-289.) 

Concerning the relation of these four forms of plastids 
to spontaneous generation, the following is the most 
probable : — 1. The simple cytods (Gymnocytoda), naked 
particles of plasma without kernel, like the still living 
Monera, are the only plastids which directly come into 
existence by spontaneous generation. 2. The enclosed cytods 
(Lepocytoda), particles of plasma without kernel, which are 
surrounded by a covering (membrane or shell), arose out of 
the simple cytods either by the condensation of the outer 
layers of plasma or by the secretion of a covering. 3. The 
simple cells (Gymnocyta), or naked cells, particles of plasma 
with kernel, but without covering, arose out of the simple 
cytods by the condensation of the innermost particles of 
plasma into a kernel, or nucleus, by differentiation of a 
central kernel and peripheral cell-substance. 4. The 
enclosed cells (Lepocyta), or testaceous cells, particles of 
plasma with kernel and an outer covering (membrane or 
shell), arose either out of the enclosed cytods by the forma- 
tion of a kernel, or out of the simple cells by the formation 
of a membrane. All the other forms of form-units, or 
plastids, met with, besides these, have only subsequently 
arisen out of these four fundamental forms by natural 
selection, by descent with adaptation, by differentiation 
and transformation. 

By this theory of plastids, by deducing all the different 
forms of plastids, and hence, also, all organisms composed 
of them, from the Monera, we obtain a simple and natural 
connection in the whole series of the development of nature. 
The origin of the first Monera by spontaneous generation 


appears to us as a simple and necessary event in the pro- 
cess of the development of the earth. We admit that this 
process, as long as it is not directly observed or repeated by 
experiment, remains a pure hypothesis. But I must again 
say that this hypothesis is indispensable for the consistent 
completion of the non-miraculous history of creation, that 
it has absolutely nothing forced or miraculous about it, 
and that certainly it can never be positively refuted. It 
must be taken into consideration that the process of spon- 
taneous generation, even if it still took place daily and 
hourly, would in any case be exceedingly difficult to observe 
and establish with absolute certainty as such. "With regard 
to the Monera, we find ourselves placed before the following 
alternative : either they are actually directly derived from 
pre-existing, or " created," most ancient Monera, and in this 
case they would have had to propagate themselves un- 
changed for many millions of years, and to have maintained 
their original form of simple particles of plasma ; or, the 
present Monera have originated much later in the course of 
the organic history of the earth, by repeated acts of spon- 
taneous generation, and in this case spontaneous generation 
may take place now as well as then. The latter suppo- 
sition has evidently much more probability on its side than 
the former. 

If we do not accept the hypothesis of spontaneous 
generation, then at this one point of the history of develop- 
ment we must have recourse to the miracle of a super- 
natural creation. The Creator must have created the first 
organism, or a few first organisms, from which all others are 
derived, and as such he must have created the simplest 
Monera, or primaeval cytods, and given them the capability 


of developing further in a mechanical way. I leave it to 
each one of my readers to choose between this idea and the 
hypothesis of spontaneous generation. To me the idea that 
the Creator should have in this one point arbitrarily inter- 
fered with the regular process of development of matter, 
which in all other cases proceeds entirely without his inter- 
position, seems to be just as unsatisfactory to a believing 
mind as to a scientific intellect. If, on the other hand, 
we assume the hypothesis of spontaneous generation for the 
origin of the first organisms, which in consequence of 
reasons mentioned above, and especially in consequence of 
the discovery of the Monera, has lost its former difficulty, 
then we arrive at the establishment of an uninterrupted 
natural connection between the development of the earth 
and the organisms produced on it, and, in this last remain- 
ing lurking-place of obscurity, we can proclaim the unity 
of all Nature, and the unity of her laws of Development 
(Gen. Morph. i. 164). 




Chorological Facts and Causes. — Origin of most Species in one Single 
Locality: "Centres of Creation." — -Distribution by Migration. — Active 
and Passive Migrations of Animals and Plants. — Means of Transport. — 
Transport of Germs by Water and by Wind. — Continual Change of the 
Area of Distribution by Elevations and Depressions of the Ground. — 
Chorological Importance of Geological Processes. — Influence of the 
Change of Climate. — Ice or Glacial Period. — Its Importance to 
Chorology. — Importance of Migrations for the Origin of New Species. 
— Isolation of Colonists. — Wagner's Law of Migration. — Connection 
between the Theory of Migration and the Theory of Selection. — Agree- 
ment of its Results with the Theory of Descent. 

As I have repeatedly said, but cannot too much emphasize, 
the actual value and invincible strength of the Theory 
of Descent does not lie in its explaining this or that single 
phenomenon, but in the fact that it explains all biological 
phenomena, that it makes all botanical and zoological 
series of phenomena intelligible in their relations to one 
another. Hence every thoughtful investigator is the more 
firmly and deeply convinced of its truth the more he 
advances from single biological observations to a general 
view of the whole domain of animal and vegetable life. 
Let us now, starting from this comprehensive point of view, 
survey a biological domain, the varied and complicated 


phenomena of which may 'be explained with remarkable 
simplicity and clearness by the theory of selection. I 
mean Chorology, or the theory of the local distribution of 
organisms over the surface of the earth. By this I do 
not only mean the geographical distribution of animal 
and vegetable species over the different parts and provinces 
of the earth, over continents and islands, seas, and rivers • 
but also their topographical distribution in a vertical 
direction, their ascending to the heights of mountains, and 
their descending into the depths of the ocean. (Gen. 
Morph. ii. 286.) 

The strange chorological series of phenomena which 
show the horizontal distribution of organisms over parts of 
the earth, and their vertical distribution in heights and 
depths, have long since excited general interest. In recent 
times Alexander Humboldt 39 and Frederick Schouw have 
especially discussed the geography of plants, and Berghaus 
and Schmarda the geography of animals, on a large scale. 
But although these and several other naturalists have in 
many ways increased our knowledge of the distribution of 
animal and vegetable forms, and laid open to us a new 
domain of science, full of wonderful and interesting 
phenomena, yet Chorology as a whole remained, as 
far as their labours were concerned, only a desultory 
knowledge of a mass of individual facts. It could not be 
called a science as long as the causes for the explanation of 
these facts were wanting. These causes were first disclosed 
by the theory of selection and its doctrine of the migrations 
of animal and vegetable species, and it is only since the 
works of Darwin and Wallace that we have been able to 
speak of an independent science of Chorology. 


If all the phenomena of the geographical and topographi- 
cal distribution of organisms are examined by themselves, 
without considering the gradual development of species, and 
if at the same time, following the customary superstition, the 
individual species of animals and plants are considered 
as forms independently created and independent of one 
another, then there remains nothing for us to do but to gaze 
at those phenomena as a confused collection of incompre- 
hensible and inexplicable miracles. But as soon as we 
leave this low stand-point, and rise to the height of the 
theory of development, by means of the supposition of a 
blood-relationship between the different species, then all 
at once a clear light falls upon this strange series of 
miracles, and we see that all chorological facts can 
be understood quite simply and clearly by the supposition of 
a common descent of the species, and their passive and 
active migrations. 

The most important principle from which we must start 
in chorology, and of the truth of which we are convinced by 
due examination of the theory of selection, is that, as a rule, 
every animal and vegetable species has arisen only once in 
the course of time and only in one place on the earth — its 
so-called " centre of creation" — by natural selection. I share 
this opinion of Darwin's unconditionally, in respect to the 
great majority of higher and perfect organisms, and in 
respect to most animals and plants in which the division of 
labour, or differentiation of the cells and organs of which 
they are composed, has attained a certain stage. For it 
is quite incredible, or could at best only be an exceedingly 
rare accident, that all the manifold and complicated circum- 
stances — all the different conditions of the struggle for life, 


which influence the origin of a new species by natural 
selection — should have worked together in exactly the 
same agreement and combination more than once in the 
earth's history, or should have been active at the same time 
at several different points of the earth's surface. 

On the other hand, I consider it to be very probable that 
certain exceedingly imperfect organisms of the simplest 
structure, forms of species of an exceedingly indifferent 
nature, as, for example, many single-celled Protista, but 
especially the Monera, the simplest of them all, should have 
several times or simultaneously arisen in their specific form 
in several parts of the .earth. For the few and very simple 
conditions by which their specific form was changed in the 
struggle for life may surely have often been repeated, in 
the course of time, independently in different parts of 
the earth. Further, those higher specific forms also, which 
have not arisen by natural selection, but by hybridism (the 
previously-mentioned hybrid species, pp. 147 and 275), may 
have repeatedly arisen anew in different localities. As, 
however, this proportionately small number of organisms 
does not especially interest us here, we may, in respect 
of chorology, leave them alone, and need only take 
into consideration the distribution of the great majority 
of animal and vegetable species in regard to which the 
single origin of every species in a single locality, in its 
so-called "central point of creation," can be considered as 
tolerably certain. 

Every animal and vegetable species from the beginning 
of its existence has possessed the tendency to spread beyond 
the limited locality of its origin, beyond the boundary of 
its " centre of creation," or, in other words, beyond its 

VOL. i. 2 a 


primceval home, or its natal place. This is a necessary 
consequence of the relations of population and over-popula- 
tion (pp. 161 and 256). The more an animal or vegetable 
species increases, the less is its limited natal place sufficient 
for its sustenance, and the fiercer the struggle for life ; the 
more rapid the over-population of the natal spot, the more 
it leads to emigration. These migrations are common to all 
organisms, and are the real cause of the wide distribution 
of the different species of organisms over the earth's surface. 
Just as men leave over-crowded states, so all animals and 
plants migrate from their over-crowded primaeval homes. 

Many distinguished naturalists, especially Lyell 11 and 
Schleiden, have before this repeatedly drawn attention to 
the great importance of these very interesting migrations of 
organisms. The means of transport by which they are 
effected are extremely varied. Darwin has discussed these 
most excellently in the eleventh and twelfth chapters of 
his work, which are exclusively devoted to " geographical 
distribution." The means of transport are partly active, 
partly passive; that is to say, the organism effects its 
migration partly by free locomotion due to its own activity, 
and partly by the movements of other natural bodies in 
which it has no active share. 

It is self-evident that active migrations play the chief 
part in animals able to move freely The more freely an 
animal's organization permits it to allmove in directions, the 
more easily the animal species can migrate, and the more 
rapidly it will spread over the earth. Flying animals are of 
course most favoured in this respect, among vertebrate animals 
especially birds, and among articulated animals, insects. 
These two classes, as soon as they came into existence, can 


have more easily spread over the whole earth than any other 
animal, and this fact partly explains the extraordinary uni- 
formity of structure which characterizes these two great 
classes of animals. For, although they contain an ex- 
ceedingly large number of different species, and although 
the insect class alone is said to possess more different species 
than all other classes of animals together, yet all the in- 
numerable species of insects, and in like manner, also, the 
different species of birds, agree most strikingly in all 
essential peculiarities of their organization. Hence, in the 
class of insects, as well as in that of birds, we can distinguish 
only a very small number of large natural groups or orders, 
and these few orders differ but very little from one another 
in their internal structure. The orders of birds with their 
numerous species are not nearly as distinct from one another 
as the orders of the mammalian class, containing much fewer 
species ; and the orders of insects, which are extremely rich 
in genera and species, resemble one another much more 
closely in their internal structure than do the much smaller 
orders of the crab class. The general parallelism between 
birds and insects is also very interesting in relation to syste- 
matic zoology; and the great importance of their richness 
in forms, for scientific morphology, lies in the fact that they 
show us how, within the narrowest anatomical sphere, and 
without profound changes of the essential internal organiz- 
ation, the greatest variety in external bodily forms can be 
attained. The reason of this is evidently their flying mode 
of life and their free locomotion. In consequence of this 
birds, as well as insects, have spread very rapidly over 
the whole surface of the earth, have settled in all possible 
localities inaccessible to other animals, and variously modified 


their specific form by superficial adaptation to particular 
local relations. 

Next to the flying animals, those animals, of course, have 
spread most quickly and furthest which were next best able 
to migrate, that is, the best runners among the inhabitants 
of the land, and the best swimmers among the inhabitants of 
the water. However, the power of such active migrations 
is not confined to those animals which throughout life enjoy 
free locomotion. For the fixed animals also, such as corals, 
tubicolous worms, sea-squirts, lily encrinites, sea-acorns, bar- 
nacles, and many other lower animals which adhere to sea- 
weeds, stones, etc., enjoy, at least at an early period of life, 
free locomotion. They all migrate before they adhere to 
anything. Their first free locomotive condition of early life 
is generally that of a " ciliated " larva, a roundish, cellular 
corpuscle, which, by means of a garb of movable " flimmer- 
hairs," (Latin, " cilia ") swarms about in the water and bears 
the name of Planula. 

But the power of free locomotion, and hence, also, of active 
migration, is not confined to animals alone, but many plants 
likewise enjoy it. Many lower aquatic plants, especially the 
class of the Tangles (Algae), swim about freely in the water 
in early life, like the lower animals just mentioned, by 
means of a vibratile hairy coat, a vibrating whip, or a 
covering of tremulous fringes, and only at a later period 
adhere to objects. Even in the case of many higher plants, 
which we designate as creepers and climbing plants, we may 
speak of active migration Their elongated stalks and 
perennial roots creep or climb during their long process 
of growth to new positions, and by means of their wide- 
spread branches they acquire new habitations, to which 


they attach themselves by buds, and bring forth new 
colonies of individuals of their species. 

Influential as these active migrations of most animals 
and many plants are, yet alone they would by no 
means be sufficient to explain the chorology of organisms. 
Passive migrations have ever been by far the more import- 
ant, and of far greater influence, in the case of most plants 
and in that of many animals. Such passive changes of 
locality are produced by extremely numerous causes. Air 
and water in their eternal motion, wind and waves with 
their manifold currents, play the chief part. The wind in 
all places and at all times raises light organisms, small 
animals and plants, but especially their young germs, animal 
eggs and plant seeds, and carries them far over land and 
seas. Where they fall into the water they are seized by 
currents or waves and carried to other places. It is well 
known, from numerous examples, how far in many cases 
trunks of trees, hard shelled fruits, and other not readily 
perishable portions of plants are carried away from their 
original home by the course of rivers and by the currents 
of the sea. Trunks of palm trees from the West Indies are 
brought by the Gulf Stream to the British and Norwegian 
coasts. All large rivers bring down driftwood from the 
mountains, and frequently alpine plants are carried from their 
home at the source of the river into the plains, and even 
further, down to the sea. Frequently numerous inhabitants 
live between the roots of the plants thus carried down, and 
between the branches of the trees thus washed away there 
are various inhabitants which have to take part in the 
passive migration. The bark of the tree is covered with 
mosses, lichens, and parasitic insects. Other insects, spiders, 


etc., even small reptiles and mammals, are hidden within 
the hollow trunk or cling to the branches. In the earth 
adhering to the fibres of the roots, in the dust lying in the 
cracks of the bark, there are innumerable germs of smaller 
animals and plants. Now, if the trunk thus washed away 
lands safely on a foreign shore or on a distant island, the 
guests who had to take part in the involuntary voyage can 
leave their boat and settle in the new country. A very 
remarkable kind of water- transport is formed by the floating 
icebergs which annually become loosened from the eternal 
ice of the Polar Sea. Although these cold regions are thinly 
peopled, yet many of their inhabitants, who were accidentally 
upon an iceberg while it was becoming loosened, are carried 
away with it by the currents, and landed on warmer shores. 
In this manner, by means of loosened blocks of ice from 
the northern Polar Sea, often whole populations of small 
animals and plants have been carried to the northern 
shores of Europe and America. Nay, even polar foxes and 
polar bears have been carried in this way to Iceland and to 
the British Isles. 

Transport by air is no less important than transport by 
water in this matter of passive migration. The dust cover- 
in«- our streets and roofs, the earth lying on dry fields and 
dried-up pools, the light moist soil of forests, in short, the 
whole surface of the globe contains millions of small organ- 
isms and their germs. Many of these small animals and 
plants can without injury become completely dried up, and 
awake again to life as soon as they are moistened. Every 
oust of wind raises up with the dust innumerable little 
creatures of this kind, and often carries them away to other 
places miles off. But even larger organisms, and especially 


their germs, may often make distant passive journeys through 
the air. The seeds of many plants are provided with light 
feathery processes, which act as parachutes and facilitate their 
flight in the air, and prevent their falling. Spiders make 
journeys of many miles through the air on their fine fila- 
ments, their so-called gossamer threads. Young frogs are 
frequently raised by whirlwinds into the air by thousands, 
and fall down in a distant part as a " shower of frogs." Storms 
may carry birds and insects across half the earth's circum- 
ference. They drop in the United States, having risen in 
England. Starting from California, they only come to rest 
in China. But, again, many other organisms may make the 
journey from one continent to another together with the 
birds and insects. Of course all parasites, the number of 
which is legion, fleas, lice, mites, moulds, etc., migrate with 
the organisms upon which they live. In the earth which 
often remains sticking to the claws of birds there are also 
small animals and plants or their germs. Thus the volun- 
tary or involuntary migration of a single larger organism 
may carry a whole small flora and fauna from one part of 
the earth to another. 

Besides the means of transport here mentioned, there 
are many others which explain the distribution of animal 
and vegetable species over the large tracts of the earth's 
surface, and especially the general distribution of the so- 
called cosmopolitan species. But these alone would not 
nearly be sufficient to explain all chorological facts. How 
is it, for example, that many inhabitants of fresh water 
live in various rivers or lakes far away and quite apart from 
one another ? How is it that many inhabitants of moun- 
tains, which cannot exist in plains, are found upon entirely 


separated and far distant chains of mountains ? It is diffi- 
cult to believe, and in many cases quite inconceivable, that 
these inhabitants of fresh water should have in any way, 
actively or passively, migrated over the land lying between 
the lakes, or that the inhabitants of mountains in any 
way, actively or passively, crossed the plains lying between 
their mountain homes. But here geology comes to our help, 
as a mighty ally, and completely solves these difficult pro- 
blems for us. 

The history of the earth's development shows us that the 
distribution of land and water on its surface is ever and 
continually changing. In consequence of geological changes 
of the earth's crust, elevations and depressions of the ground 
take place everywhere, sometimes more strongly marked in 
one place, sometimes in another. Even if they happen so 
slowly that in the course of centuries the seashore rises or 
sinks only a few inches, or even only a few lines, still they 
nevertheless effect great results in the course of long periods 
of time. And long — immeasurably long — periods of time 
have not been wanting in the earth's history. During the 
course of many millions of years, ever since organic life ex- 
isted on the earth, land and water have perpetually struggled 
for supremacy. Continents and islands have sunk into the 
sea, and new ones have arisen out of its bosom. Lakes and 
seas have slowly been raised and dried up, and new water 
basins have arisen by the sinking of the ground. Peninsulas 
have become islands by the narrow neck of land which con- 
nected them with the mainland sinking into the water. 
The islands of an archipelago have become the peaks of a 
continuous chain of mountains by the whole floor of their 
sea being considerably raised. 


Thus the Mediterranean at one time was an inland sea, 
when, in the place of the Straits of Gibraltar, an isthmus 
connected Africa with Spain. England, even during the 
more recent history of the earth, when man already 
existed, has repeatedly been connected with the European 
continent and been repeatedly separated from it. Nay, 
even Europe and North America have been directly 
connected. The South Sea at one time formed a 
large Pacific Continent, and the numerous little islands 
which now lie scattered in it were simply the highest 
peaks of the mountains covering that continent. The 
Indian Ocean formed a continent which extended from 
the Sunda Islands along the southern coast of Asia to 
the east coast of Africa. This large continent of former 
times Sclater, an Englishman, has called Lemuria, from the 
monkey-like animals which inhabited it, and it is at the 
same time of great importance from being the probable 
cradle of the human race, which in all likelihood here first 
developed out of anthropoid apes. The important proof 
which Alfred Wallace has furnished, 30 by the help of 
chorological facts, that the present Malayan Archipelago 
consists in reality of two completely different divisions, 
is particularly interesting. The western division, the Indo- 
Malayan Archipelago, comprising the large islands of 
Borneo, Java, and Sumatra, was formerly connected by 
Malacca with the Asiatic continent, and probably also with 
the Lemurian continent just mentioned. The eastern 
division, on the other hand, the Austro-Malayan Archipelago, 
comprising Celebes, the Moluccas, New Guinea, Solomon's 
Islands, etc., was formerly directly connected with Austra- 
lia. Both divisions were formerly two continents separated 


by a strait, but they have now for the most part sunk 
below the level of the sea. Wallace, solely on the ground of 
his accurate chorological observations, has been able in the 
most acute manner to determine the position of this former 
strait, the south end of which passes between Balij and 

Thus, ever since liquid water existed on the earth, the 
boundaries of water and land have eternally changed, and 
we may assert that the outlines of continents and islands 
have never remained for an hour, nay, even for a minute; 
exactly the same. For the waves eternally and perpetually 
break on the edge of the coast, and whatever the land in 
these places loses in extent, it gains in other places by the 
accumulation of mud, which condenses into solid stone and 
again rises above the level of the sea as new land. Nothing 
can be more erroneous than the idea of a firm and 
unchangeable outline of our continents, such as is im- 
pressed upon us in early youth by defective lessons on 
geography, which are devoid of a geological basis. 

I need hardly draw attention to the fact that these 
geological changes of the earth's surface have ever been ex- 
ceedingly important to the migrations of organisms, and 
consequently to their Chorology. From them we learn to 
understand how it is that the same or nearly related species of 
animals and plants can occur on different islands, although 
they could not have passed through the water separating 
them, and how other species living in fresh water can inhabit 
different enclosed water -basins, although they could not have 
crossed the land lying between them. These islands were 
formerly mountain peaks of a connected continent, and 
these lakes were once directly connected with one another. 


The former were separated by geological depressions 
the latter by elevations. Now, if we further consider how 
often and how unequally these alternating elevations and 
depressions occur on the different parts of the earth, and how, 
in consequence of this, the boundaries of the geographical 
tracts of distribution of species become changed, and if 
we further consider in what exceedingly various ways the 
active and passive migrations of organisms must have been 
influenced by them, then we shall be in a position to com- 
pletely understand the great variety of the picture which 
is at present offered to us by the distribution of animal 
and vegetable species. 

There is yet another important circumstance to be men- 
tioned here, which is likewise of great importance for a 
complete explanation of this varied geographical picture, 
and which throws light upon many very obscure facts, 
which, without its help, we should not be able to compre- 
hend. I mean the gradual change of climate which has 
taken place during the long course of the organic history of 
the earth. As we saw in our last chapter, at the beginning 
of organic life on the earth a much higher and more equal 
temperature must have generally prevailed than at present. 
The differences of zones, which in our time are so very 
striking, did not exist at all in those times. It is probable 
that for many millions of years but one climate prevailed 
over the whole earth, which very closely resembled, or even 
surpassed, the hottest tropical climate of the present day. 
The highest north which man has yet reached was then 
covered with palms and other tropical plants, the fossil re- 
mains of which are still found there. The temperature of 
this climate at a later period gradually decreased ; but still 


the poles remained so warm that the whole surface of the 
earth could be inhabited by organisms. It was only at a 
comparatively very recent period of the earth's history, 
namely, at the beginning of the tertiary period, that there 
occurred, as it seems, the first perceptible cooling of the 
earth's crust at the poles, and through this the first differen- 
tiation or separation of the different zones of temperature 
or climatic zones. But the slow and gradual decrease of 
temperature continued to extend more and more within the 
tertiary period, until at last, at both poles of the earth, the 
first permanent ice caps were formed. 

I need scarcely point out in detail how very much this 
change of climate must have affected the geographical dis- 
tribution of organisms, and the origin of numerous new 
species. The animal and vegetable species, which, down 
to the tertiary period, had found an agreeable tropical 
climate all over the earth, even as far as the poles, 
were now forced either to adapt themselves to the in- 
truding cold, or to flee from it. Those species which 
adapted and accustomed themselves to the decreasing 
temperature became new species simply by this very accli- 
matization, under the influence of natural selection. The 
other species, which fled from the cold, had to emigrate and 
seek a milder climate in lower latitudes. The tracts of dis- 
tribution which had hitherto existed must by this have 
been vastly changed. 

However, during the last great period of the earth's 
history, during the quaternary period (or diluvial period) 
succeeding the tertiary one, the decrease of the heat 
of the earth from the poles did not by any means remain 
stationary. The temperature fell lower and lower, nay, even 


far below the present degree. Northern and Central Asia, 
Europe, and North America from the north pole, were 
covered to a great extent by a connected sheet of ice, which 
in our part of the earth seems to have reached the Alps. 
In a similar manner the cold also advancing from the south 
pole covered a large portion of the southern hemisphere, 
which is now free from it, with a rigid sheet of ice. Thus, 
between these vast lifeless ice continents there remained 
only a narrow zone to which the life of the organic world 
had to withdraw. This period, during which man, or at 
least the human ape, already existed, and which forms the 
first period of the so-called diluvial epoch, is now universally 
known as the ice or glacial period. 

The ingenious Carl Schimper is the first naturalist who 
clearly conceived the idea of the ice period, and proved the 
great extent of the former glaciation of Central Europe by 
the help of the so-called boulders, or erratic blocks of stone, 
as also by the " glacier tables." Louis Agassiz, stimulated 
by him, and considerably supported by the independent 
investigations of the eminent geologist Charpentier, after- 
wards undertook the task of carrying out the theory of the 
ice period. In England, the geologist Forbes distinguished 
himself in this matter, and also was the first to apply it 
to the theory of migrations and the geographical distribu- 
tion of species dependent upon migration. Agassiz, however, 
afterwards injured the theory by his one-sided exaggeration, 
inasmuch as, from his partiality to Cuvier's theory of cata- 
clysms, he endeavoured to attribute the destruction of the 
whole animate creation then existing, to the sudden coming 
on of the cold of the ice period and the " revolution " con- 
nected with it. 


It is unnecessary here to enter into detail as to the ice 
period itself, and into investigations about its limits, and 
I may omit this all the more reasonably since the whole 
of our recent geological literature is full of it. It will be 
found discussed in detail in the works of Cotta, 31 Lyell, 30 
Vogt, 27 Zittel, 32 etc. Its great importance to us here is 
that it helps us to explain the most difficult chorological 
problems, as Darwin has correctly perceived. 

For there can be no doubt that this glaciation of the 
present temperate zones must have exercised an exceedingly 
important influence on the geographical and topographical 
distribution of organisms, and that it must have entirely 
changed it. While the cold slowly advanced from the poles 
towards the equator, and covered land and sea with a con- 
nected sheet of ice, it must of course have driven the whole 
living world before it. Animals and plants had to migrate 
if they wished to escape being frozen. But as at that time 
the temperate and tropical zones were probably no less 
densely peopled with animals and plants than at present, 
there must have arisen a fearful struggle for life between 
the latter and the intruders coming from the poles. During 
this struggle, which certainly lasted many thousands of 
years, many species must have perished and many become 
modified and been transformed into new species. The 
hitherto existing tracts of distribution of species must have 
become completely changed, and the struggle have been 
continued, nay, indeed, must have broken out anew and 
been carried on in new forms, when the ice period had 
reached and gone beyond its furthest point, and when in 
the post-glacial period the temperature again increased, and 
organisms began to migrate back again towards the poles. 


In any case this great change of climate, whether a 
greater or less importance be ascribed to it, is one of 
those occurrences in the history of the earth which have 
most powerfully influenced the distribution of organic 
forms. But more especially one important and difficult 
chorological circumstance is explained by it in the simplest 
manner, namely, the specific agreement of many of our 
Alpine inhabitants with some of those living in polar 
regions. There is a great number of remarkable animal 
and vegetable forms which are common to these two far 
distant parts of the earth, and which are found nowhere 
in the wide plains lying between them. Their migration 
from the polar lands to the Alpine heights, or vice versa, 
would be inconceivable under the present climatic circum- 
stances, or could be assumed at least only in a few rare 
instances. But such a migration could take place, nay, 
was obliged to take place, during the gradual advance and 
retreat of the ice-sheet. As the glaciation encroached from 
Northern Europe towards our Alpine chains, the polar in- 
habitants retreating before it — gentian, saxifrage, polar 
foxes, and polar hares — must have peopled Germany, in 
fact all Central Europe. When the temperature again in- 
creased, only a portion of these Arctic inhabitants returned 
with the retreating ice to the Arctic zones. Another portion 
of them climbed up the mountains of the Alpine chain 
instead, and there found the cold climate suited to them. 
The problem is thus solved in a most simple manner. 

We have hitherto principally considered the theory of the 
migrations of organisms in so far as it explains the radiation 
of every animal and vegetable species from a single pri- 
maeval home, from a " central point of creation," and the 


dispersion of these species over a greater or less portion of 
the earth's surface. But these migrations are also of great 
importance to the theory of development, because we can 
perceive in them a very important means for the origin of 
'new species. When animals and plants migrate they meet in 
their new home, in the same way as do human emigrants, 
with conditions which are more or less different from those 
which they have inherited throughout generations, and to 
which they have been accustomed. The emigrants must 
either submit and adapt themselves to these new conditions 
of life or they perish. By adaptation their peculiar specific 
character becomes the more changed the greater the dif- 
ference between the new and the old home. The new 
climate, the new food, but above all, new neighbours in 
the forms of other animals and plants, influence and tend 
to modify the inherited character of the immigrant species, 
and if it is not hardy enough to resist the influences, then 
sooner or later a new species must arise out of it. In most 
cases this transformation of an immigrant species takes 
place so quickly under the influence of the altered struggle 
for life, that even after a few generations a new species 
arises from it. 

Migration has an especial influence in this way on all 
organisms with separate sexes. For in them the origin of 
new species by natural selection is always rendered difficult, 
or delayed, by the fact that the modified descendants oc- 
casionally again mix sexually with the unchanged original 
form, and thus by crossing return to the first form. But 
if such varieties have migrated, if great distances or 
barriers to migration — seas, mountains, etc. — have separated 
them from the old home, then the danger of a mingling 


with the primary form is prevented, and the isolation of 
the emigrant form, which becomes a new species by adapta- 
tion, prevents its breeding with the old stock, and hence 
prevents its return in this way to the original form. 

The importance of migration for the isolation of newly- 
originating species and the prevention of a speedy return to 
the primary form has been especially pointed out by the 
philosophic traveller, Moritz Wagner, of Munich. In a 
special treatise on " Darwin's Theory and the Law of the 
Migration of Organisms," ^ Wagner gives from his own 
rich experience a great number of striking examples which 
confirm the theory of migration set forth by Darwin in 
the eleventh and twelfth chapters of his book, where he es- 
pecially discusses the effect of the complete isolation of emi- 
grant organisms in the origin of new species. Wagner sets 
forth the simple causes which have " locally bounded the 
form and founded its typical difference," in the following 
three propositions : — 1. The greater the total amount of 
change in the hitherto existing conditions of life which the 
emigrating individuals find on entering a new territory, the 
more intensely must the innate variability of every organ- 
ism manifest itself. 2. The less this increased individual 
variability of organisms is disturbed in the peaceful process 
of reproduction by the mingling of numerous subsequent 
immigrants of the same species, the more frequently will 
nature succeed, by intensification and transmission of the 
new characteristics, in forming a new variety or race, that is, 
a commencing species. 3. The more advantageous the 
changes experienced by the individual organs are to the 
variety, the more readily will it be able to adapt itself 
to the suiTOunding conditions; and the longer the undis- 

VOL. I. 2 B 


turbed breeding of a commencing variety of colonists in a 
new territory continues without its mingling with subse- 
quent immigrants of the same species, the oftener a new 
species will arise out of the variety." 

Every one will agree with these three propositions of 
Moritz Wagner's. But we must consider his view, that the 
migration and the subsequent isolation of the emigrant in- 
dividuals is a necessary condition for the origin of new 
species, to be completely erroneous. Wagner says, " with 
out a long-enduring separation of colonists from their former 
species, the formation of a new race cannot succeed — selection, 
in fact, cannot take place. Unlimited crossing, unhindered 
sexual mingling of all individuals of a species will always 
produce uniformity, and drive varieties, whose characteris- 
tics have not been fixed throughout a series of generations, 
back to the primary form." 

This sentenge, in which Wagner himself comprises the 
main result of bis investigations, he would be able to defend 
only if all organisms were of separate sexes, if every origin 
of new individuals were possible only by the mingling of 
male and female individuals. But this is by' no means 
the case. Curiously enough, Wagner says nothing of 
the numerous hermaphrodites which, possessing both the 
sexual organs, are capable of self-fructification, and like- 
wise nothing of the countless organisms which are not 
sexually differentiated. 

Now, from the earliest times of the organic history of the 
earth, there have existed thousands of organic species 
(thousands of which still exist) in which no difference of 
sex whatever exists, and, in fact, in which no sexual propa- 
gation takes place, and which exclusively reproduce them- 


selves in a non-sexual manner by division, budding, for- 
mation of spores, etc. All the great mass of Protista, the 
Monera, Amcebse, Myxomycetes, Khizopoda, etc., in short, 
all the lower organisms which we shall have to enumerate 
in the domain of Protista, standing midway between the 
animal and vegetable kingdoms, propagate themselves 
exclusively in a non-sexual manner. And this domain 
comprises a class of organisms which is one of the richest 
in forms, nay, even in a certain respect the richest of all 
in forms, as all possible geometrical fundamental forms are 
represented in it. I allude to the wonderful class of the 
Rhizopoda, or Ray-streamers, to which the lime-shelled 
Acyttaria and the flint-shelled Radiolaria belong. (Com- 
pare chapter xvi.) 

It is self-evident, therefore, that Wagners theory is quite 
inapplicable to all these non-sexual organisms. Moreover, 
the same applies to all those hermaphrodites in which 
every individual possesses both male and female organs and 
is capable of self-fructification. This is the case, for instance, 
in the Flat-worms, flukes, and tapeworms, further in the 
important Sack-worms (Tunicates), the invertebrate relatives 
of the vertebrate animals, and in very many other organisms 
of different groups. Many of these species have arisen by 
natural selection, without a " crossing " of the originating 
species with its primary form having been possible. 

As I have already shown in the eighth chapter, the 
origin of the two sexes, and consequently sexual propagation 
in general, must be considered as a process which began only 
in later periods of the organic history of the earth, being 
the result of differentiation or division of labour. The most 
ancient terrestrial organisms can have propagated themselves 


only in the simplest non-sexual manner. Even now all 
Protista, as well as all the countless forms of cells, which 
constitute the body of higher organisms, multiply themselves 
only by non-sexual generation. And yet there arise here 
" new species " by differentiation in consequence of natural 

But even if we were to take into consideration the animal 
and vegetable species with separate sexes, in this case too 
we should have to oppose Wagner's chief proposition, that 
" the "migration of organisms and their formation of colonies 
is the necessary condition of natural selection." August 
Weismann, in his treatise on the "Influence of Isolation 
upon the Formation of Species," 24 has already sufficiently 
refuted that proposition, and has shown that even in one 
and the same district one bi-sexual species may divide itself 
into several species by natural selection. In relation to this 
question, I must again call to mind the great influence 
which division of labour, or differentiation, possesses, being 
one of the necessary results of natural selection. All 
the different kinds of cells constituting the body of the 
higher organisms, the nerve cells, muscle cells, gland cells, 
etc., all these " good species," these " bonae species " of 
elementary organisms, have arisen solely by division of 
labour, in consequence of natural selection, although they 
not only never were locally isolated, but ever since their 
origin have always existed in the closest local relations one 
with another. Now, the same reasoning that applies to these 
elementary organisms, or " individuals of the first order," 
applies also to the many-celled organisms of a higher order 
which only at a later date have arisen as " good species " 
from among their fellows. 


We are therefore of the same opinion as Darwin and 
Wallace, that the migration of organisms and their isolation 
in their new home is a very advantageous condition for the 
origin of new species; but we cannot admit, as Wagner 
asserts, that it is a necessary condition, and that without it 
no species can arise. Wagner sets up this opinion, " that 
migration is a necessary condition for natural selection," as a 
special " law of migration " \ but we consider it sufficiently 
refuted by the above-mentioned facts. We have, moreover, 
already pointed out that in reality the origin of new species 
by natural selection is a mathematical and logical necessity 
which, without anything else, follows from the simple com- 
bination of three great facts. These three fundamental 
facts are — the Struggle for Life, the Adaptability, and the 
Hereditivity of organisms. 

We cannot here enter into detail concerning the numerous 
interesting phenomena furnished by the geographical and 
topographical distribution of organic species, which are all 
wonderfully explained by the theory of selection and 
migration For these I refer to the writings of Darwin, 1 
Wallace, 36 and Moritz Wagner, 40 in which the im- 
portant doctrine of the limits of distribution — seas, rivers, 
and mountains — is excellently discussed and illustrated by 
numerous examples. Only three other phenomena must 
be mentioned here on account of their special importance. 
First, the close relation of forms, that is, the striking " family 
likeness " existing between the characteristic local forms of 
every part of the globe, and their extinct fossil ancestors in 
the same part of the globe ; secondly, the no less striking 
" family likeness " between the inhabitants of island groups 
and those of the neighbouring continent from which the 


islands were peopled; lastly and thirdly, the peculiar 
character presented in general by the flora and fauna of 
islands taken as a whole. 

All these chorological facts given by Darwin, Wallace, 
and Wagner — especially the, remarkable phenomena of the 
limited local fauna and flora, the relations of insular to conti- 
nental inhabitants, the wide distribution of the so-called 
"cosmopolitan species," the close relationship of the local 
species of the present day with the extinct species of the 
same limited territory, the demonstrable radiation of 
every species from a single central point of creation — all 
these, and all other phenomena furnished to us by the 
geographical and the topographical distribution of organisms, 
are explained in a simple and thorough manner by the 
theory of selection and migration, while without it they are 
simply incomprehensible. Consequently, in the whole of 
this series of phenomena we find a new and weighty proof 
of the truth of the Theory of Descent. 


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